Systems and methods for transmitting electromagnetic energy over a wireless channel having sufficiently weak measured signal strength

ABSTRACT

A signal strength that is associated with a first wireless communications channel is detected. Electromagnetic energy is transmitted over the first wireless communications channel in response to the signal strength being sufficiently weak. A determination is made whether a handoff should be made to a second wireless communications channel having a signal that is weaker than a signal of the first wireless communications channel. Related systems and methods are described.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/965,303, filed Oct. 14, 2004, entitled Integrated or AutonomousSystem and Method of Satellite-Terrestrial Frequency Reuse Using SignalAttenuation and/or Blockage, Dynamic Assignment of Frequencies and/orHysteresis, which itself is a continuation of U.S. application Ser. No.10/000,799, filed Dec. 4, 2001, now U.S. Pat. No. 6,859,652, entitledIntegrated or Autonomous System and Method of Satellite-TerrestrialFrequency Reuse Using Signal Attenuation and/or Blockage, DynamicAssignment of Frequencies and/or Hysteresis, and claims priority fromU.S. provisional Application Ser. No. 60/250,461, filed Dec. 4, 2000,entitled System and Method of Satellite-Terrestrial Frequency Reuse. Allof these applications are assigned to the assignee of the presentapplication, the disclosures of which are hereby incorporated herein byreference in their entirety as if set forth fully herein.

FIELD OF THE INVENTION

The present invention generally relates to frequency assignment, reuseand/or sharing among communications systems having both a terrestrialcomponent and a satellite component and, more particularly, to asatellite-terrestrial communication system and method of operationthereof that provides frequency assignment, reuse and/or sharing betweenautonomously operating or integrated satellite and terrestrialcomponents, that can optionally utilize different communicationprotocols and/or air interfaces.

DESCRIPTION OF THE RELATED ART

FIG. 1 shows a prior art satellite radiotelephone system, as shown inU.S. Pat. No. 6,052,586, incorporated herein by reference. As shown inFIG. 1, a satellite radiotelephone system includes a fixed satelliteradiotelephone system 110 and a mobile satellite radiotelephone system130. The fixed satellite radiotelephone system 110 uses a firstsatellite 112 to communicate with a plurality of fixed radiotelephones114 a, 114 b and 114 c in a first communication area 116.

Fixed satellite radiotelephone communication system 110 communicateswith the plurality of fixed radiotelephones 114 a-114 c using a firstair interface 118 (e.g., at C-band). Control of the fixed satellitesystem 110 is implemented by a feeder link 122 which communicates with agateway 124 and the public switched (wire) telephone network (PSTN) 126.

The feeder link 122 includes communication channels for voice and datacommunications, and control channels. The control channels are indicatedby dashed lines in FIG. 1. The control channels are used to implementdirect communications between fixed radiotelephones, as shown forexample between radiotelephones 114 a and 114 b. The control channelsare also used to effect communications between a fixed satelliteradiotelephone 114 c and a mobile radiotelephone or a wire telephone viagateway 124 and PSTN 126. The feeder link 122 uses the same airinterface or a different air interface from the first air interface 118.

Still referring to FIG. 1, mobile satellite radiotelephone system 130includes a second satellite 132 that communicates with a plurality ofmobile radiotelephones 134 a-134 d which are located in a secondcommunication area 136. Mobile satellite radiotelephone system 130communicates with mobile radiotelephones 134 using a second airinterface 138 (e.g., at L-band or S-band). Alternatively, the second airinterface 138 may be the same as the first air interface 118. However,the frequency bands associated with the two air interfaces aredifferent.

A feeder link 142 is used to communicate with other satellite, cellularor wire telephone systems via gateway 144 and PSTN 126. As with fixedsatellite system 110, the feeder link 142 includes communicationchannels shown in solid lines and control channels shown in dashedlines. The control channels are used to establish directmobile-to-mobile communications, for example, between mobileradiotelephones 134 b and 134 c. The control channels are also used toestablish communications between mobile phones 134 a and 134 d and othersatellite, mobile or wire telephone systems.

As with the fixed satellite radiotelephone system 110, the mobilesatellite radiotelephone system 130 will generally communicate withlarge numbers of mobile radiotelephones 134. The fixed and mobilesatellite radiotelephone system use a common satellite.

Still referring to FIG. 1, a congested area may be present in the mobilesatellite radiotelephone system 130 where a large number of mobileradiotelephones 134 e-134 i are present. As is also shown in FIG. 1,this congested area may be in an overlapping area 128 between firstcommunication area 116 and second communication area 136. If this is thecase, excess capacity from fixed satellite radiotelephone system 110 isoffloaded to mobile satellite radiotelephone system 130.

Capacity offload is provided by at least one fixed retransmittingstation 150 a, 150 b, that retransmits communications between the fixedsatellite radiotelephone system 110 and at least one of the mobileradiotelephones. For example, as shown in FIG. 1, first fixedretransmitting station 150 a retransmits communications betweensatellite 112 and mobile radiotelephones 134 e and 134 f. Second fixedtransmitting station 150 b retransmits communications between thesatellite 112 and mobile radiotelephones 134 g, 134 h and 134 i.

The fixed retransmitting stations communicate with the satellite 112using first air interface 118. However they communicate with the mobileradiotelephones using the second air interface 138. Accordingly, fromthe standpoint of the mobile radiotelephones 134 e-134 i, communicationis transparent. In other words, it is not apparent to the mobileradiotelephones 134 e-134 i, or the users thereof, that communicationsare occurring with the fixed satellite radiotelephone system 110 ratherthan with the mobile satellite radiotelephone system 130. However,additional capacity for the mobile satellite radiotelephone system 130in the congested areas adjacent the fixed retransmitting stations 150 isprovided.

As shown in FIG. 1, a mobile radiotelephone can establish acommunications link via the facilities of the fixed satelliteradiotelephone system, even though the mobile radiotelephone isdesigned, manufactured and sold as a terminal intended for use with themobile satellite radiotelephone system. One or more operators may offerboth mobile and fixed telecommunications services over an overlappinggeographic area using two separate transponders in separate satellitesor within the same “hybrid” satellite, with one transponder supportingmobile satellite radiotelephones and the other supporting fixedsatellite radiotelephones. As capacity “hot spots” or congestiondevelops within certain spot beams of the mobile radiotelephone system,the fixed system, with its much higher capacity, can deploy fixedretransmitting stations to relieve the capacity load of the mobilesystem.

FIG. 2A shows a seven-cell frequency reuse pattern used by the mobilesatellite radiotelephone system 130. Within each of the relatively largemobile system cells, each typically being on the order of 400-600kilometers in diameter, frequencies used by adjacent cells are locallyretransmitted by the retransmitting station at reduced, non-interferingpower levels, and reused as shown in FIGS. 2B and 2C, thus substantiallyincreasing the effective local capacity.

Accordingly, fixed retransmitting stations 150 a, 150 b, located withinthe fixed system's footprint or coverage area, receive signals from thefixed satellite and retransmit these signals locally. In the reversedirection, the fixed retransmitting stations receive signals from mobileradiotelephones 134 e-i and retransmit signals from the mobileradiotelephones to the fixed satellite system 110. Frequency translationto bring the signals within the fixed system's frequency band isprovided.

The mobile radiotelephones 134 e-i are ordinarily used with the mobilesatellite system 130. Accordingly, the fixed satellite system 110 mayneed to be configured to support the air interface used by the mobilesatellite radiotelephone system. If different air interfaces are used bythe fixed and mobile satellite radiotelephone systems, the fixedretransmitting stations 150 a, 150 b, can perform a translation from oneair interface to the other, for example, by demodulation andremodulation. The fixed retransmitting station then becomes aregenerative repeater which reformats communications channels as well ascontrol channels. However, if the mobile and fixed systems both usesubstantially the same air interface, then the fixed retransmittingstation can function as a non-regenerative repeater.

However, in contrast to U.S. Pat. No. 6,052,586, the present inventiondoes not utilize in at least one embodiment frequency translationbetween fixed and mobile systems. Also in contrast to U.S. Pat. No.6,052,586, the present invention optionally provides autonomous orsubstantially autonomous operation between the satellite and terrestrialcomponents.

FIG. 3 is another prior art system as shown in U.S. Pat. No. 5,995,832,incorporated herein by reference. FIG. 3 provides an overview of acommunications system 310 showing the functional inter-relationships ofthe major elements. The system network control center 312 directs thetop level allocation of calls to satellite and ground regional resourcesthroughout the system. It also is used to coordinate system-wideoperations, to keep track of user locations, to perform optimumallocation of system resources to each call, dispatch facility commandcodes, and monitor and supervise overall system health. The regionalnode control centers 314, one of which is shown, are connected to thesystem network control center 312 and direct the allocation of calls toground nodes within a major metropolitan region. The regional nodecontrol center 314 provides access to and from fixed land communicationlines, such as commercial telephone systems known as the public switchedtelephone network (PSTN). The ground nodes 316, under direction of therespective regional node control center 314, receive calls over thefixed land line network, encode them, spread them according to theunique spreading code assigned to each designated user, combine theminto a composite signal, modulate that composite signal onto thetransmission carrier, and broadcast them over the cellular regioncovered.

Satellite node control centers 318 are also connected to the systemnetwork control center 312 via status and control land lines andsimilarly handle calls designated for satellite links such as from PSTN,encode them, spread them according to the unique spreading codesassigned to the designated users, and multiplex them with othersimilarly directed calls into an uplink trunk, which is beamed up to thedesignated satellite 320. Satellite nodes 320 receive the uplink trunks,frequency demultiplex the calls intended for different satellite cells,frequency translate and direct each to its appropriate cell transmitterand cell beam, and broadcast the composite of all such similarlydirected calls down to the intended satellite cellular area. As usedherein, “backhaul” means the link between a satellite 320 and asatellite node control center 318.

User units 322 respond to signals of either satellite or ground nodeorigin, receive the outbound composite signal, separate out the signalintended for that user by despreading using the user's assigned uniquespreading code, de-modulate, and decode the information and deliver thecall to the user. Such user units 322 may be mobile or may be fixed inposition. Gateways 324 provide direct trunks (i.e., groups of channels)between satellite and the ground public switched telephone system orprivate trunk users. For example, a gateway may comprise a dedicatedsatellite terminal for use by a large company or other entity. In theembodiment of FIG. 3, the gateway 324 is also connected to that systemnetwork controller 312.

All of the above-discussed centers, nodes, units and gateways are fullduplex transmit/receive performing the corresponding inbound (user tosystem) link functions as well in the inverse manner to the outbound(system to user) link functions just described.

FIG. 4 is a block diagram of U.S. Pat. No. 5,995,832 which does notinclude a system network control center 312. In this system, thesatellite node control centers 442 are connected directly into the landline network as are also the regional node control centers 444. Gatewaysystems 446 are also available as in the system of FIG. 3, and connectthe satellite communications to the appropriate land line or othercommunications systems. The user unit 322 designates satellite node 442communication or ground node 450 communication by sending apredetermined code. Alternatively, the user unit could first search forone type of link (either ground or satellite) and, if that link ispresent, use it. If that link is not present, use the alternate type oflink.

U.S. Pat. No. 5,995,832 uses code division multiple access (CDMA)technology to provide spectral utilization and spatial frequency reuse.The system of U.S. Pat. No. 5,995,832 has a cluster size of one. Thatis, each cell uses the same, full allocated frequency band. This ispossible because of the strong interference rejection properties ofspread spectrum code division multiple access technology (SS/CDMA).

The specification of U.S. Pat. No. 5,595,832 also states that in aspread spectrum system, the data modulated carrier signal is modulatedby a relatively wide-band, pseudo-random “spreading” signal so that thetransmitted bandwidth is much greater than the bandwidth or rate of theinformation to be transmitted, and that the “spreading” signal isgenerated by a pseudo-random deterministic digital logic algorithm whichis duplicated at the receiver. In this regard, FIG. 7 of U.S. Pat. No.5,995,832 discloses PRN generators 136, 166 in conjunction with wideband multipliers 122, 148 that are associated with CDMA technology.

The system also determines the position of user units 322 throughtwo-dimensional multi-lateration. Each CDMA mobile user unit'stransmitted spreading code is synchronized to the epoch of reception ofthe pilot signal from its current control site, whether ground orsatellite node.

However, it has been determined that it is desirable to havecommunication protocols other than CDMA be used in asatellite-terrestrial system. It is also desirable to have asatellite-terrestrial system that does not require frequency translationbetween fixed and mobile systems. In addition, it is also desirable toprovide a satellite-terrestrial system that does not require CDMAtechnology, and which utilizes a robust satellite-terrestrial frequencyassignment and/or reuse scheme in which the satellite and terrestrialcomponents can optionally utilize different air interfaces, andoptionally operate independently of each other while either sharing acommon or different frequency band.

Further, it is also desirable to provide a satellite-terrestrial systemthat utilizes a first frequency as a downlink frequency between asatellite and a first fixed and/or mobile user terminal and as an uplinkfrequency between a second fixed and/or mobile user terminal and aterrestrial base transceiver station (BTS), and a second frequency as anuplink between the first fixed and/or mobile user terminal and thesatellite and as a downlink between the BTS and the second fixed and/ormobile user terminal. Other advantages and features of the invention aredescribed below, that may be provided independently and/or in one ormore combinations.

It is also desirable to provide a satellite-terrestrial system in whichthe space based and ground based components function autonomously orsubstantially autonomously in which the space based component can use atime division multiple access (TDMA) air interface, and the ground basedsystem can use either a TDMA air interface or a CDMA air interface. Insuch a system, it is further desirable to provide user units having afirst plurality of vocoders, each having a different data rate, and asecond plurality of vocoders, each having a different data rate, whereina vocoder in the first plurality is used when the subscriber terminal iscommunicating with the space based system, and wherein a vocoder in thesecond plurality is used when the subscriber terminal is communicatingwith the ground based system.

SUMMARY OF THE INVENTION

It is one feature and advantage of the present invention to provide asatellite-terrestrial communication system in which the satellite andterrestrial components utilize different air interfaces whilefacilitating efficient spectrum assignment, usage, sharing, and/orreuse.

It is another optional feature and advantage of at least someembodiments of the present invention to provide a satellite-terrestrialcommunication system in which the satellite and terrestrial componentsoperate independently of each other while sharing at least a portion,and optionally all, of a common frequency band.

It is another optional feature and advantage of at least someembodiments of the present invention to provide a satellite-terrestrialcommunication system in which the satellite and terrestrial componentsoperate independently of each other while utilizing discrete frequencybands.

It is another optional feature and advantage of at least someembodiments of the present invention to provide a satellite-terrestrialcommunications system and method of operation thereof that minimizesinterference between the satellite and terrestrial components.

It is another optional feature and advantage of at least someembodiments of the present invention to provide a communication systemutilizing at least two air interfaces having a common area of coverage,wherein at least a portion of the frequencies associated with a firstair interface are assigned, reused and/or shared by the second airinterface.

It is still another optional feature and advantage of at least someembodiments of the present invention to provide a satellite-terrestrialcommunication system in which frequencies are assigned, used and/orreused when signal strength is, for example, attenuated and/or blockedby terrain and/or structures.

It is still another optional feature and advantage of at least someembodiments of the present invention to provide a satellite-terrestrialcommunication system that dynamically assigns frequencies.

It is yet another feature and advantage of at least some embodiments ofthe present invention to provide a satellite-terrestrial communicationsystem that utilizes hysteresis and/or negative hysteresis in assigning,re-assigning and/or reusing frequencies.

It is another optional feature and advantage of at least someembodiments of the present invention to, for example, invert thefrequencies between the satellite system and an underlay terrestrialsystem, whereby a first frequency is used, for example, as a downlinkfrequency between a satellite and a first fixed and/or mobile userterminal, and as an uplink frequency between a second fixed and/ormobile user terminal and a BTS. In addition, a second frequency is used,for example, as an uplink between the first fixed and/or mobile userterminal, and the satellite and as a downlink between the BTS and thesecond fixed and/or mobile user terminal.

The present invention provides a system and method for assigning,re-assigning, using and/or reusing channels for terrestrial and/orsatellite use. In one embodiment, a satellite-terrestrial communicationsystem and method is provided for reusing one or more channels in amanner that minimizes interference between the respective satellite andterrestrial systems. The present invention can also be applied tomultiple satellite systems as well as, in addition to, or instead of,terrestrial systems. The present invention optionally provides both aterrestrial frequency assignment and/or reuse plan, and a satellitefrequency assignment and/or reuse plan.

Advantageously, the present invention provides a satellite-terrestrialsystem and method that optionally uses a reduction in signal strengthcaused by, for example, signal attenuation, terrain blocking and/orblocking by man-made structures to assign, use or reuse one or morechannels. In one embodiment, the channels having the weakest signal arereused terrestrially in order to minimize interference.

Another embodiment determines that one or more of the satellite channelsdetected by, for example, a subscriber terminal or BTS are not beingused. In this embodiment, any idle channels are preferably usedterrestrially first before any used (i.e., established) satellitechannels are considered for terrestrial reuse.

The satellite and terrestrial components can operate in an integratedmanner, or autonomously. For example, in an integrated embodiment, thesatellite and terrestrial components can share a common networkoperations controller (NOC), mobile switching center (MSC), and/or RadioResource Manager (RRM). In an autonomous embodiment, a separate NOC, MSCand/or RRM is provided for each of the satellite and terrestrialcomponents. For example, a RRM associated with the terrestrial componentcan comprise or utilize, for example, a suitable antenna operativelyconnected to a spectrum analyzer and/or other signal detection means tosearch a band of radio frequencies for the presence of radio signals, todetermine what frequencies are currently being utilized within a rangeor ranges of frequencies of interest. The terrestrial RRM can thereforedetermine, independently and without communication with a RRM associatedwith the satellite component, or any other satellite componentequipment, what frequencies are not being used by the system. Since theterrestrial RRM knows the frequencies used across a range of frequenciesof interest, as well as the frequencies used by the terrestrialcomponent, the terrestrial RRM can also determine or deduce thefrequencies that are currently being used by the satellite component.Similarly, the satellite component functions in substantially the samemanner to, inter alia, determine the frequencies currently being used bythe terrestrial component.

In the case of, for example, a single geosynchronous satellite havingmultiple spot beams, the channels that are reassigned terrestrially canbe predetermined and/or computed dynamically. In the case of multiplesatellites, a predetermined preference may optionally be provided wherethe subscriber terminals communicate by using either the satellitesystem or the terrestrial system.

In another embodiment, the present invention minimizes the frequencyreuse between the satellite and terrestrial networks by utilizingchannels for each system in an ordered manner. Channels can bedynamically reassigned to maximize frequency separation and therebyminimize any potential interference therebetween.

In another embodiment, the invention optionally uses hysteresis so thatthere is a predetermined difference in signal strength before allowing asubscriber terminal to transition back and forth between channelsassociated with, for example, two adjacent spot beams or BTSs.Similarly, the present invention optionally uses negative hysteresis tokeep channels assigned to, for example, a BTS having a weaker signalstrength rather than, handing off to another channel having a strongersignal strength. Negative hysteresis can also be used, for example, tofacilitate a desired loading of the respective satellite and/orterrestrial networks, either individually or in combination with eachother.

In yet another embodiment, the present invention uses a MSC tocoordinate frequency assignment and/or use between the satellite andterrestrial components. The MSC determines which of the channels arecurrently being used, and where. In this embodiment, the MSC isoperatively communicable with, for example, a base station controller(BSC) which, in turn, informs one or more BTSs which channels arecurrently in use by the satellite component. When a channel goes in useon a satellite while the channel is being used terrestrially, adetermination is made whether a handoff should be made to a channelhaving a weaker signal.

More particularly, at least one embodiment of the present inventioncomprises a space based system comprising at least one satellite. Eachsatellite, in turn, comprises at least one antenna and establishes afirst set of cells and transmits and receives GSM based waveforms usingat least a first portion or at least one predetermined frequency bandused by the first set of cells. In addition, a ground based systemcomprises at least one base transceiver station (BTS), each which canestablish a second set of cells and transmit and receive GSM basedwaveforms utilizing at least a second portion of the one predeterminedfrequency band. The space and ground systems function substantiallyautonomously and use and/or reuse at least a portion of spectrum from atleast one predetermined frequency band to be used as at least one of anuplink and downlink frequency channel from any of the frequencies withinthe at least one predetermined frequency band. However, the space basedsystem and ground based system can utilize any air interfaces. Forexample, in other embodiments, the space and ground based systems canoptionally utilize, for example, a code division multiple access (CDMA)based air interface or derivatives thereof. Similarly, the space basedsystem can optionally utilize a CDMA based air interface or derivativethereof, whereas the ground based system can optionally utilize a GSMbased air interface or derivative thereof. In addition, the ground basedsystem can optionally utilize a CDMA based air interface or derivativethereof, whereas the space based system can optionally utilize a GSMbased air interface or derivative thereof.

The system further comprises at least one subscriber terminal thatcommunicates with at least one of the space based system and with theground based system when located in at least one of the first and secondset of cells, as well as at least one RRM that determines availablecommunication links between the at least one subscriber terminal and atleast one of the space based system and the ground based systems.

The at least one predetermined frequency band optionally comprises atleast one discrete space based system uplink portion and at least onediscrete space based system downlink portion, wherein the ground basedsystem uses and/or reuses at least a portion of at least one of theuplink and downlink portions. Each of the discrete portions areoptionally associated with at least one of a satellite spot beam and asubsection of a spot beam.

The at least one predetermined frequency band optionally comprises atleast one discrete space based system uplink portion, at least onediscrete space based system downlink portion, and at least ground basedsystem portion. Further, at least two cells of the first set of cells inthe space based system optionally utilize a mutually exclusive portionof the first portion of the at least one predetermined frequency band.

One or more frequencies in the first and second portion of the at leastone predetermined frequency band used by the space based system and theground based system are optionally substantially the same or closelyspaced.

Each of the subscriber terminals can optionally utilize at least a firstvocoder having a first data rate and at least a second vocoder having asecond data rate, wherein the first vocoder is used when a subscriberterminal is communicating with the space based system, and wherein thesecond vocoder is used when the subscriber terminal is communicatingwith the ground based system. The RRM optionally assigns and/oractivates at least one of the first and second vocoders in response topredetermined criteria such as capacity demand, voice quality, and/orreceived signal level.

The system can also optionally utilize at least one MSC that isoperatively connected to the space based system and the ground basedsystem that at assigns and/or activates a vocoder in response topredetermined criteria such as capacity demand, voice quality, andreceived signal level. The RRM can also optionally assign or activate adifferent vocoder to a voice communications circuit in response to thepredetermined criteria such as capacity demand, voice quality, signalstrength, and received signal level having changed substantially sinceassignment or activation of the at least first and second vocoder beingutilized.

The at least one predetermined frequency band can optionally comprisefirst and second frequency bands, such that subscriber terminalscommunicate with the ground based system by transmitting at firstfrequencies within the first frequency band used as an uplink of thespace based system, and receive at second frequencies within the secondfrequency band used as a downlink of the space based system. Inaddition, the first and second frequencies used by a cell of the spacebased system are optionally mutually exclusive to third frequencies usedby a cell of the ground based system containing one or more of thesubscriber terminals, within the cell of the space based system.

The at least one predetermined frequency band can also optionallycomprise first and second frequency bands, such that subscriberterminals communicate with the ground based system by transmitting atfirst frequencies within a first frequency band used as a downlink ofthe space based system, and receive at second frequencies within asecond frequency band used as an uplink of the space based system. Thefirst and second frequencies used by a cell of the space based systemare mutually exclusive to third frequencies used by a cell of the groundbased system containing one or more of the subscriber terminals, withinthe cell of said space based system.

The at least one predetermined frequency band can also optionallycomprise first and second frequency bands, such that subscriberterminals communicate with the ground based system(s) by transmitting atfirst frequencies within the first frequency band used as the uplink ofthe space based system, and receive at frequencies within the firstfrequency band used as the uplink of the space based system. The firstand second frequencies used by a cell of the space based system areoptionally mutually exclusive to third frequencies used by a cell of theground based system containing one or more of the subscriber terminals,within the cell of said space based system.

The at least one predetermined frequency band can also optionallycomprise first and second frequency bands, such that subscriberterminals communicate with the ground based system(s) by transmitting atfirst frequencies within the first frequency band used as the downlinkof the space based system, and receive at frequencies within the firstfrequency band used as the downlink of the space based system. The firstand second frequencies used by a cell of the space based system areoptionally mutually exclusive to third frequencies used by a cell of theground based system containing one or more of the subscriber terminals,within the cell of the space based system.

The RRM(s) can optionally monitor which channels are currently beingutilized by the subscriber terminals. A MSC operatively connected to oneor more of the RRMs can optionally be utilized, wherein one or more ofthe RRMs indicate to the MSC which channels are currently being utilizedby one or more of the subscriber terminals. Each RRM, can be, forexample, a spectrum analyzer. Individual RRMs can optionally be utilizedin connection with each of the space based and ground based systems to,for example, monitor inband interference and avoid using and/or reusingchannels that would cause levels of interference exceeding apredetermined threshold. The RRMs can also optionally monitor at leastone of received signal quality and available link margin from one ormore of the subscriber terminals. The RRMs can also optionally executeutilization of a different communications channel when a quality measureof the existing communications channel has fallen below a predeterminedlevel or has fallen below a predetermined link margin.

Each of the subscriber terminals can optionally comprise a variable ratevocoder, or two or more vocoders each having a different data rate. Thevocoder data rate can be selected as determined by predeterminedcriteria such as capacity demand, voice quality, signal strength, and/orreceived signal level.

RRMs can optionally monitors inband interference and avoid usingchannels containing levels of interference exceeding a predeterminedthreshold, as well as monitor received signal quality from subscriberterminals communicating with the space based system and/or ground basedsystem. RRMs can also optionally monitor available link margin fromsubscriber terminals communicating with the space based and/or groundbased systems. The RRMs can also optionally execute utilization of adifferent communications channel when a quality measure of the existingcommunications channel has fallen below a predetermined level or hasfallen below a predetermined link margin.

The system can optionally comprise a NOC operatively connected to atleast a MSC that assigns a channel to subscriber units. The NOCmaintains cognizance of the availability of satellite and/or terrestrialresources, and optionally administers at least one of reconfiguration,assignment and reuse of frequencies within the predetermined frequencyband to meet changed traffic patterns or other predetermined conditions.The NOC is optionally commonly shared between and operatively connectedto the space based and ground based systems. The NOC can also optionallyutilize past system traffic patterns in the reconfiguration, assignmentand/or reuse of the frequencies, as well as utilize at least one ofhysteresis and negative hysteresis in the reconfiguration, assignmentand/or reuse of the frequencies.

The space based system satellite can optionally have a geostationaryorbit, wherein the NOC dynamically assigns a channel to a subscriberunit communicating with the space based system. The dynamic assignmentcan optionally be performed on a call-by-call basis, or be based on pastand present usage. Dynamic assignment is optionally performed by one ormore base station controllers operationally connected to the NOC.

A exemplary method in accordance with the present invention assigns to arequesting subscriber unit a communication channel commonly sharedbetween a space based communication system and a ground basedcommunication system. The method comprises the steps of configuring afirst satellite spot beam, associated with the space based system,having a plurality of communication channels associated therewith, andconfiguring at least one terrestrial cell, associated with the groundbased system, that at least partially geographically overlaps the firstsatellite spot beam. A dual mode subscriber terminal requests acommunication channel, and at least one of the ground based system andthe space based system substantially autonomously determines channelavailability and assigns to the requesting dual mode subscriber unit atleast one of an unused channel and, for reuse with the dual modesubscriber terminal, a used channel having a sufficiently weak signalstrength.

In accordance with the method, the space based system optionallyutilizes a time division multiple access (TDMA) air interface, and theground based system optionally utilizes a TDMA air interface. Ingeneral, however, any first and second air interfaces can berespectively utilized by the space based and ground based systems. Forexample, the first air interface can optionally be a GSM based airinterface or a derivative thereof, and the second air interface canoptionally be a GSM based air interface or a derivative thereof.Alternatively, the first air interface can optionally be a GSM based airinterface or a derivative thereof, and the second air interface canoptionally be a CDMA based air interface or a derivative thereof.Similarly, the first air interface can optionally be a CDMA based airinterface or a derivative thereof, and the second air interface canoptionally be a GSM based air interface or a derivative thereof.Further, the first air interface can optionally be a CDMA based airinterface or a derivative thereof, and the second air interface canoptionally be a CDMA based air interface or a derivative thereof.

The method optionally further comprises the step of increasing theoutput power of a subscriber terminal utilizing the space based systemas the composite signal strength of the subscriber terminals utilizingthe ground based system reaches a predetermined threshold. The number ofsubscriber terminals connections with the ground based system canoptionally be decreased as at least one of bit error rate, receivedsignal strength, available link margin, and voice quality reachrespective predetermined thresholds.

The method optionally further comprises the steps of enabling asubscriber terminal to communicate at a plurality of data rates, andselecting a data rate as determined by at least one of capacity demand,voice quality, and subscriber terminal received signal level. One ormore subscriber terminals communicating with the space based or groundbased system can optionally utilize a different data rate as determinedby at least one of capacity demand, and received signal level havingchanged substantially since assignment or activation of the currentchannel.

The channel can optionally comprise first and second frequency bands,such that the subscriber terminals communicate with the ground basedsystem by transmitting at first frequencies within the first frequencyband used as an uplink of the space based system, and receive at secondfrequencies within the second frequency band used as a downlink of thespace based system. Subscriber terminals can also communicates with theground based system by transmitting at first frequencies within a firstfrequency band used as an uplink of the space based system, and receiveat second frequencies within a second frequency band used as a downlinkof the space based system. Subscriber terminal can also optionallycommunicate with the ground based system by transmitting at firstfrequencies within a first frequency band used as the uplink of thespace based system, and receive at first frequencies within the firstfrequency band used as the uplink of the space based system. Inaddition, subscriber terminals can also optionally communicate with theground based system by transmitting at first frequencies within a firstfrequency band used as the downlink of the space based system, andreceive at first frequencies within the first frequency band used as thedownlink of the space based system. Further, subscriber terminals canoptionally communicate with the ground based system by transmitting atfirst frequencies within a first frequency band used as the downlink ofthe space based system, and receive at first frequencies within thefirst frequency band used as the downlink of the space based system.

In accordance with the method, a first communication channel associatedwith the space based system optionally comprises a first frequency bandused for uplink communication and a second frequency band used foruplink communication, such that the ground based system shares at leasta common portion of the first and second frequency bands in aterrestrial cell positioned outside of and non-overlapping with thesatellite spot beam.

In accordance with the method, at least one of the ground based systemand the space based system optionally autonomously monitors inbandinterference and avoids using and/or reusing channels that would causelevels of interference exceeding a predetermined threshold. A differentcommunications channel is preferably utilized when a quality measure ofthe existing communications channel has fallen below a predeterminedlevel.

In accordance with the method, at least one of the space based systemand the ground based systems autonomously monitor at least one ofreceived signal quality and available link margin from a subscriberterminal. A different communications channel is preferably utilized whenat least one of received signal quality and available link margin hasfallen below a predetermined link margin.

The method optionally further comprises the step of arranging for atleast one of channel reconfiguration and reuse of frequencies to meetchanged traffic patterns. Past system traffic patterns, hysteresisand/or negative hysteresis can optionally be utilized in determining thereconfiguration and reuse of frequencies.

In accordance with the method, the communication channel is optionallyassigned to the subscriber unit in accordance with a predeterminedchannel assignment scheme.

Also in accordance with the present invention, a method of making atelephone call using at least one of a space based system and a groundbased system comprises the steps of dialing by a user using a subscriberterminal a telephone number within an area of a first terrestrial cellhaving at least partial overlapping geographic coverage with at least asatellite spot beam, wherein the terrestrial cell and the spot beamshare a common set of frequencies. At least one of the ground basedsystem and the space based system substantially autonomously determineschannel availability in response to the dialing, and assign a channel tothe requesting subscriber terminal.

In another embodiment, the system in accordance with the presentinvention comprises a cellular-configured dual mode communicationssystem comprising a space based system comprising a first set of cells,and a ground based system comprising a second set of cells. Embodimentsof the present invention contemplate that the space and ground systemscan function in an integrated manner or substantially autonomously, eachembodiment optionally using spectrum from, for example, the same set offrequencies in at least one predetermined frequency band and/ordifferent sets of frequencies in one or more discrete bands, optionallydedicated to a particular system.

In at least some embodiments, two cells of the space based system use amutually exclusive portion of the at least one predetermined frequencyband. The space based system can optionally utilize a TDMA airinterface, and the ground based system can also utilize a TDMA airinterface. The TDMA air interfaces can be a standard GSM air interfaceor a derivative and/or similar system thereof. In general, however, thespace based and ground based systems can utilize any first and secondair interfaces. For example, the space based system can utilize a GSMbased air interface or a derivative thereof, and the ground based systemcan utilize a CDMA based air interface or a derivative thereof. Inaddition, the space based system can utilize a CDMA based air interfaceor a derivative thereof, and the ground based system can utilize a CDMAbased air interface or a derivative thereof. Further, the space basedsystem can utilize a GSM based air interface or a derivative thereof,and the ground based system can utilize a CDMA based air interface or aderivative thereof.

The at least one predetermined frequency band can optionally comprise atleast one of a discrete space based system uplink portion and a discretespace based system downlink portion. The ground based system canoptionally utilize at least a portion of at least one of the uplink anddownlink portions, wherein each of the discrete portions are optionallyassociated with at least one of a satellite spot beam and a subsectionof a spot beam.

The at least one predetermined frequency band further optionallycomprises a discrete ground based system portion, wherein at least twocells of said space based system optionally utilize a mutually exclusiveportion of the at least one predetermined frequency band.

The system further comprises at least one subscriber terminalcommunicating with the space based system and with the ground basedsystem. The at least one predetermined frequency band used by the spacebased system and the ground based system are optionally substantiallythe same.

Subscriber terminals comprise having means for communicating with thespace based system and with the ground based system optionally include afirst plurality of standard vocoders, each having a different data rate,and a second plurality of standard vocoders, each having a differentdata rate. A vocoder in the first plurality can be used when asubscriber terminal is communicating with the space based system, and avocoder in the second plurality can be used when a subscriber terminalis communicating with the ground based system. The subscriber terminalscan also utilize a variable rate vocoder.

The system can also include a RRM that assigns a vocoder or otherfunctionally similar device in response to predetermined criteria suchas capacity demand, voice quality and/or received signal level. The RRMcan optionally assign a different vocoder to a voice communicationscircuit in response to predetermined criteria such as capacity demandand/or received signal level having changed substantially sinceassignment of the vocoder utilized.

Subscriber terminals can optionally communicate with the ground basedsystem by transmitting at frequencies within a frequency band used as anuplink of the space based system, and receiving at frequencies within afrequency band used as a downlink of the space based system. In anotherembodiment of the present invention, the subscriber terminalscommunicate with the ground based system by transmitting at frequencieswithin a frequency band used as a downlink of the space based system,and receiving at frequencies within a frequency band used as an uplinkof the space based system. The subscriber terminals can also optionallycommunicate with the ground based system by transmitting at frequencieswithin a frequency band used as an uplink of the space based system, andreceiving at frequencies within a frequency band used as the uplink ofthe space based system. Further, the subscriber terminals can optionallycommunicate with the ground based system by transmitting at frequencieswithin a frequency band used as the downlink of the space based system,and receive at frequencies within a frequency band used as the downlinkof the space based system. In each of the above embodiments of thepresent invention, the frequencies used by a cell of the space basedsystem can optionally be mutually exclusive to those used by a cell ofthe ground based system, containing one or more of subscriber terminals,within the cell of the space based system.

At least some embodiments of the system in accordance with the presentinvention can utilize one or more RRMs that monitor which channels arecurrently being utilized by each or any of one or more subscriberterminals. A first RRM can be utilized in connection with the groundbased system, and a second RRM can be utilized in connection with thespace based system. In at least some embodiments of the presentinvention, the one or more RRMs monitor inband interference and avoidusing and/or reusing channels that would cause levels of interferenceexceeding a predetermined threshold. The one or more RRMs can optionallymonitor subscriber terminal received signal quality, available linkmargin and/or utilization of a different communications channel when aquality measure of the existing communications channel has fallen belowa predetermined level and/or has fallen below a predetermined linkmargin. The one or more RRMs also monitor inband interference and avoidusing channels containing levels of interference exceeding apredetermined threshold, and/or monitor available link margin fromsubscriber terminals communicating with at least one of the space basedsystem and the ground based system. In accordance with at least someembodiments of the present invention, the one or more RRMs can alsoexecute utilization of a different communications channel when a qualitymeasure of the existing communications channel has fallen below apredetermined level or has fallen below a predetermined link margin.

The RRM(s) can optionally monitor which channels are currently beingutilized by the subscriber terminals. A MSC operatively connected to oneor more of the RRMs can optionally be utilized, wherein one or more ofthe RRMs indicate to the MSC which channels are currently being utilizedby one or more of the subscriber terminals. Each RRM, can be, forexample, a spectrum analyzer. Individual RRMs can optionally be utilizedin connection with each of the space based and ground based systems to,for example, monitor inband interference and avoid using and/or reusingchannels that would cause levels of interference exceeding apredetermined threshold. The RRMs can also optionally monitor at leastone of received signal quality and available link margin from one ormore of the subscriber terminals. The RRMs can also optionally executeutilization of a different communications channel when a quality measureof the existing communications channel has fallen below a predeterminedlevel or has fallen below a predetermined link margin.

The system can optionally comprise a NOC operatively connected to atleast a MSC that assigns a channel to subscriber units. The NOCmaintains cognizance of the availability of satellite and/or terrestrialresources, and optionally administers reconfiguration, assignment and/orreuse of frequencies within the predetermined frequency band to meetchanged traffic patterns or other predetermined conditions. The NOC isoptionally commonly shared between and operatively connected to thespace based and ground based systems. The NOC can also optionallyutilize past system traffic patterns in the reconfiguration, assignmentand/or reuse of the frequencies, as well as utilize at least one ofhysteresis and negative hysteresis in the reconfiguration, assignmentand/or reuse of the frequencies.

The space based system satellite can optionally have a geostationaryorbit, wherein the NOC dynamically assigns a channel to a subscriberunit communicating with the space based system. The dynamic assignmentcan optionally be performed on a call-by-call basis, or be based on pastand present usage. Dynamic assignment is optionally performed by one ormore base station controllers operationally connected to the NOC.

In another embodiment, the system in accordance with the presentinvention comprises a space based system comprising a first set ofcells, and a ground based system comprising a second set of cells,wherein at least a portion of the second set of cells share at least aportion of a common geographic area and have overlapping coverage withthe first set of cells, the space and ground systems functionsubstantially autonomously and each use at least a portion of commonlyshared spectrum from at least one predetermined frequency band.

The at least one predetermined frequency band optionally comprises atleast one discrete space based system uplink portion, and at least onediscrete space based system downlink portion. The ground based systemoptionally utilizes at least a portion of at least one of the uplink anddownlink portions. Each of the at least one discrete uplink and downlinkportions are optionally associated with at least one of a satellite spotbeam and a subsection of a spot beam. Further, at least two cells of thespace based system use a mutually exclusive portion of the at least onepredetermined frequency band.

The first and second air interfaces can optionally be, for example, TDMAair interfaces, such as GSM or a derivative thereof. However, ingeneral, the space based system can utilize a first air interface (e.g.,GSM or CDMA, or derivatives thereof), and the ground based system canutilize a second air interface (e.g., GSM or CDMA, or derivativesthereof).

The system further optionally comprises at least one subscriber terminalcommunicating with the space based system and with said ground basedsystem. The subscriber terminals can optionally utilize a first vocoderhaving a first data rate and a second vocoder having a second data rate,wherein first vocoder is used when a subscriber terminal iscommunicating with the space based system, and wherein a second vocoderis used when a subscriber terminal is communicating with the groundbased system.

The system further optionally comprises a RRM operatively connected tothe space based system and the ground based system, wherein the RRMoptionally assigns and/or activates at least one of the first and secondvocoders in response to, for example, capacity demand, voice quality,and/or received signal level.

The system further optionally comprises at least one MSC operativelyconnected to the space based system and the ground based system thatselectively assigns a vocoder in response to predetermined criteria suchas capacity demand, voice quality, and/or received signal level. The RRMalso optionally assigns and/or activates a different vocoder to a voicecommunications circuit in response to the predetermined criteria such ascapacity demand, voice quality, signal strength, and/or received signallevel having changed substantially since assignment or activation of theat least first and second vocoder being utilized.

The at least one predetermined frequency band optionally comprises firstand second frequency bands, and the subscriber terminals optionallycommunicate with the ground based system by transmitting at firstfrequencies within the first frequency band used as an uplink of thespace based system, and receive at second frequencies within the secondfrequency band used as a downlink of said space based system.

The subscriber terminals can also optionally communicate with the groundbased system by transmitting at first frequencies within a firstfrequency band used as a downlink of the space based system, and receiveat second frequencies within a second frequency band used as an uplinkof the space based system. The subscriber terminals can also optionallycommunicate with the ground based system by transmitting at firstfrequencies within the first frequency band used as the uplink of thespace based system, and receive at second frequencies within the secondfrequency band used as the uplink of the space based system. Further,the subscriber terminals can also optionally communicate with the groundbased system by transmitting at first frequencies within the firstfrequency band used as the downlink of the space based system, andreceive at second frequencies within the second frequency band used asthe downlink of the space based system.

The system further optionally comprises at least one RRM that monitorswhich channels are currently being utilized by each of one or moresubscriber terminals. The system further optionally comprises a MSCoperatively connected to one or more of the RRMs, wherein one or more ofthe RRMs indicates to the MSC which channels are currently beingutilized by the subscriber terminals. The RRM independently andautonomously identifies which channels are being used by the groundbased system as being the difference between all of the frequenciesbeing used by the system and the frequencies being used by said spacebased system. The RRM also independently and autonomously identifieswhich channels are being used by the space based system as being thedifference between all of the frequencies being used by the system andthe frequencies being used by said ground based system.

The system also optionally comprises a MSC operatively connected to oneor more of the RRM(s), wherein one or more of the RRM(s) indicate to theMSC which channels are currently being utilized by each of one or moresubscriber terminals. The RRM(s) can be, for example, a spectrumanalyzer.

First and second RRMs can also be utilized, wherein a first RRM isutilized in connection with the ground based system, and wherein asecond RRM is utilized in connection with the space based system. Thefirst and second RRMs monitor inband interference and avoid using and/orreusing channels that would cause levels of interference exceeding apredetermined threshold. The RRMs also monitor at least one ofsubscriber terminal received signal quality and available link margin,and also optionally execute utilization of a different communicationschannel when a quality measure of the existing communications channelhas fallen below a predetermined level and/or has fallen below apredetermined link margin. The RRMs further optionally monitor availablelink margin from subscriber terminals communicating with at least one ofthe space based system and the ground based system.

The system optionally further comprises a NOC operatively connected toat least a MSC that assigns a channel to subscriber units. The NOCmaintains cognizance of the availability of at least one of satelliteand terrestrial resources and administers reconfiguration, assignmentand/or reuse of frequencies within said predetermined frequency band tomeet changed traffic patterns or other predetermined conditions. The NOCis optionally commonly shared between and operatively connected to thespace based system and the ground based system. The NOC optionallyutilizes past system traffic patterns in the reconfiguration, assignmentand/or reuse of the frequencies, and also optionally utilizes hysteresisand/or negative hysteresis in the reconfiguration, assignment and/orreuse of the frequencies.

The system can optionally utilize a satellite having a geostationaryorbit, wherein the NOC dynamically assigns a channel to a subscriberunit communicating with the space based system and the satellite. Thedynamic assignment is optionally performed on a call-by-call basis, orbased on past and present usage. Further, the dynamic assignment isoptionally performed by one or more base station controllersoperationally connected to the NOC, such that the dynamic assignmentoptionally maximizes bandwidth separation of frequencies used by thespace based system and the ground based system.

Further, in an embodiment wherein the space based and ground basedsystems function substantially autonomously and each use one or moremutually exclusive predetermined frequency bands, a method in accordancewith the present invention is provided for initiating a call between asubscriber terminal and at least one of the space based system and theground based system. The method comprises the steps of a subscriberterminal transmitting to the system a signal indicating whether it is asingle or dual mode terminal. The system determines, based on at leastthe transmitted signal, whether the subscriber terminal is a single modeor a dual mode terminal. For a dual mode subscriber terminal, the systemat least one of assigns to the ground based system for use with the dualmode subscriber terminal an unused space based system channel, using inthe ground based system an unused ground based system channel, reusingin the ground based system a channel used by the space based systemhaving a substantially weak signal relative to the dual mode subscriberterminal, and using in the space based system a channel assigned to thespace based system. For a single mode subscriber terminal, an availablechannel is used in the space based system having an acceptable signalstrength.

Further, in a cellular communications system in which the space basedsystem and the ground based system share and commonly use at least aportion of a predetermined frequency band, and in which the space basedand ground based systems function substantially autonomously, a methodis provided for initiating a call between a subscriber terminal and atleast one of the space based system and the ground based system. Themethod comprises the steps of a subscriber terminal transmitting to thesystem a signal indicating whether it is a single or dual mode terminal.The system determines whether the subscriber terminal is a single modeor a dual mode terminal. For a dual mode subscriber terminal, the systemat least one of uses an unused channel to establish communicationbetween the ground based system and the dual mode subscriber terminal,reuses in the ground based system a channel used by the space basedsystem having a substantially weak signal relative to the subscriberterminal to establish communication between the ground based system andthe dual mode subscriber terminal, and reuses in the ground based systema channel used by the ground based system having a substantially weaksignal relative to the subscriber terminal to establish communicationbetween the ground based system and the dual mode subscriber terminal.For a single mode terminal, the space based system uses an availablechannel having an acceptable signal strength.

Further, in a cellular communications system comprising a space basedsystem comprising a first set of cells, and a ground based systemcomprising a second set of cells, in which at least a portion of thesecond set of cells share a common geographic area and have at least aportion of overlapping geographic coverage with the first set of cells,and in which the space based and ground based systems functionsubstantially autonomously and each use one or more mutually exclusivepredetermined frequency bands, a method is provided for executing ahandoff from a first base station associated with the ground system toat least one of a second base station associated with the ground basedsystem and a satellite. The method comprises the steps of determiningwhether a received signal strength indication (RSSI) between thesubscriber terminal and the second base station is satisfied. Asubscriber terminal transmits to the system a signal indicating whetherit is a single or dual mode terminal. The system determines, based on atleast the transmitted signal, whether the subscriber terminal is asingle mode or a dual mode terminal. For a dual mode subscriberterminal, when the second base station has an acceptable RSSI, thesystem at least one of reassigns to the second base station forcommunication with the dual mode subscriber terminal at least one of anunused space based system channel and an unused ground based systemchannel, and reuses by the second base station for communication withthe dual mode subscriber terminal a channel used by the space basedsystem having a substantially weak signal relative to the subscriberterminal. For a single mode subscriber terminal, the subscriber terminaluses a channel associated with the space based system having anacceptable signal strength.

Further, in a cellular communications system comprising a space basedsystem comprising a first set of cells, and a ground based systemcomprising a second set of cells, in which the space based system andthe ground based system share and commonly use at least a portion of apredetermined frequency band, the space based and ground based systemsfunctioning substantially autonomously, a method is provided forexecuting a handoff from a first base station associated with the groundsystem to at least one of a second base station associated with theground based system and a satellite. The method comprises the steps ofdetermining whether a received signal strength indication (RSSI) betweenthe subscriber terminal and the second base station is satisfied. Asubscriber terminal transmits to the system a signal indicating whetherit is a single or dual mode terminal. The system determines, based atleast one the transmitted signal, whether the subscriber terminal is asingle mode or a dual mode terminal. For a dual mode subscriberterminal, when the second base station has an acceptable RSSI, thesystem at least one of reassigns to the second base station forcommunication with the dual mode subscriber terminal an unused systemchannel, and reuses by the second base station for communication withthe dual mode subscriber terminal a channel used by the space basedsystem having a substantially weak signal relative to the subscriberterminal. For a single mode subscriber terminal, the subscriber terminaluses at least one of an unused channel and a used channel having asufficiently weak signal strength relative to the subscriber terminal.

Further, in a cellular communications system comprising a space basedsystem comprising a first set of cells, and a ground based systemcomprising a second set of cells, in which at least a portion of thesecond set of cells share a common geographic area and have at least aportion of overlapping geographic coverage with the first set of cells,the space based and ground based systems functioning substantiallyautonomously and each using one or more mutually exclusive predeterminedfrequency bands, a method is provided for executing a handoff from afirst satellite spot beam associated with the space based system to atleast one of a second satellite spot beam associated with the spacebased system and a base station associated with the ground based system.The method comprises the steps of determining whether a received signalstrength indication (RSSI) between the subscriber terminal and thesecond satellite spot beam is satisfied. A subscriber terminal transmitsto the system a signal indicating whether the subscriber terminal is asingle mode or a dual mode terminal. The system, based on at least thetransmitted signal, determines whether the subscriber terminal is asingle mode or a dual mode terminal. For a dual mode subscriberterminal, when the base station has an acceptable RSSI, the system atleast one of assigns to the base station for communication with the dualmode subscriber terminal an unused space based system channel associatedwith the second spot beam, reuses by the base station for communicationwith the dual mode subscriber terminal a channel used by the second spotbeam having a substantially weak signal strength relative to the dualmode subscriber terminal, and reuses by the base station forcommunication with the dual mode subscriber terminal a channel used bythe ground based system having a substantially weak signal strengthrelative to the dual mode subscriber terminal, and uses by the basestation for communication with the dual mode subscriber terminal anunused ground based system channel having sufficient signal strength.For a single mode subscriber terminal, a channel associated with asecond spot beam of the space based system having a acceptable signalstrength is utilized.

Further, in a cellular communications system comprising a space basedsystem comprising a first set of cells, and a ground based systemcomprising a second set of cells, in which the space based system andthe ground based system share and commonly use at least a portion of apredetermined frequency band, the space based and ground based systemsfunctioning substantially autonomously and each using at least a portionof spectrum from at least a portion of one predetermined frequency band,a method is provided for executing a handoff from a first satellite spotbeam associated with the space based system to at least one of a secondsatellite spot beam associated with the space based system and a basestation associated with the ground based system comprises the steps ofdetermining whether a received signal strength indication (RSSI) betweenthe subscriber terminal and the second base station is satisfied. Thesubscriber terminal transmits to the system a signal indicating whetherthe subscriber terminal is a single or a dual mode terminal. The systemdetermines based on at least the transmitted signal whether thesubscriber terminal is a single mode or a dual mode terminal. For a dualmode subscriber terminal, when the base station has an acceptable RSSI,the system at least one of reassigns to the base station forcommunication with the dual mode subscriber terminal an unused systemchannel, and reuses by the base station for communication with the dualmode subscriber terminal a channel used by the space based system havinga substantially weak signal relative to the dual mode subscriberterminal, reuses by the base station for communication with the dualmode subscriber terminal a channel used by the ground based systemhaving a substantially weak signal relative to the dual mode subscriberterminal. For a single mode subscriber terminal, at least one of anunused channel associated with the second spot beam and a used channelhaving a sufficiently weak signal strength relative to the subscriberterminal is utilized.

Another embodiment of the system comprises a space based systemcomprising means for establishing a first set of cells and transmittingand receiving GSM based waveforms using at least a first portion of atleast one predetermined frequency band used by the first set of cells. Aground based system comprises means for establishing a second set ofcells and transmitting and receiving GSM based waveforms utilizing atleast a second portion of the one predetermined frequency band, thespace based and ground based systems functioning substantiallyautonomously and at least one of using and reusing at least a portion ofspectrum from at least one predetermined frequency band. At least onesubscriber terminal communicates with at least one of the space basedsystem and with the ground based system when located in at least one ofthe first and second set of cells. Means for determining availablecommunication links between the at least one subscriber terminal and thespace based system and the ground based system is also provided.

The at least one predetermined frequency band optionally comprises atleast one discrete space based system uplink portion and at least onediscrete space based system downlink portion, wherein the ground basedsystem uses and/or reuses at least a portion of at least one of theuplink and downlink portions. Each of the discrete portions areoptionally associated with at least one of a satellite spot beam and asubsection of a spot beam.

The at least one predetermined frequency band optionally comprises atleast one discrete space based system uplink portion, at least onediscrete space based system downlink portion, and at least one groundbased system portion.

At least two cells of the first set of cells in the space based systemoptionally use a mutually exclusive portion of the first portion of theat least one predetermined frequency band. Further, one or morefrequencies in the first and second portion of the at least onepredetermined frequency band used by the space based system and theground based system are optionally substantially the same or closelyspaced.

The at least one subscriber terminal optionally comprises at least afirst vocoder having a first data rate and at least a second vocoderhaving a second data rate, wherein the first vocoder is used when thesubscriber terminal is communicating with the space based system, andwherein the second vocoder is used when the subscriber terminal iscommunicating with the ground based system.

The means for determining available communication links optionally atleast one of assigns and activates at least one of the first and secondvocoders in response to predetermined criteria such as capacity demand,voice quality, and/or received signal level. The means for determiningavailable communication links further optionally assigns or activates adifferent vocoder to a voice communications circuit in response to thepredetermined criteria such as such as voice quality, signal strength,and/or received signal level having changed substantially sinceassignment or activation of the first or second vocoder being utilized.

The at least one predetermined frequency band optionally comprises firstand second frequency bands, and the subscriber terminals communicatewith the ground based system by transmitting at first frequencies withinthe first frequency band used as an uplink of the space based system,and receiving at second frequencies within the second frequency bandused as a downlink of the space based system.

The first and second frequencies used by a cell of the space basedsystem are optionally mutually exclusive to third frequencies used by acell of the ground based system containing one or more of the subscriberterminals, within the cell of the space based system.

The at least one predetermined frequency band optionally comprises firstand second frequency bands, wherein the subscriber terminals communicatewith the ground based system by transmitting at first frequencies withina first frequency band used as a downlink of the space based system, andreceiving at second frequencies within a second frequency band used asan uplink of the space based system.

The first and second frequencies used by a cell of the space basedsystem are optionally mutually exclusive to third frequencies used by acell of the ground based system containing one or more of the subscriberterminals, within the cell of said space based system.

The at least one predetermined frequency band optionally comprises firstand second frequency bands, wherein the subscriber terminals communicatewith the ground based system by transmitting at first frequencies withinthe first frequency band used as the uplink of the space based system,and receives at frequencies within the first frequency band used as theuplink of the space based system.

The first and second frequencies used by a cell of the space basedsystem are optionally mutually exclusive to third frequencies used by acell of the ground based system containing one or more of the subscriberterminals, within the cell of the space based system.

The at least one predetermined frequency band optionally comprises firstand second frequency bands, wherein subscriber terminals communicatewith the ground based system by transmitting at first frequencies withinthe first frequency band used as the downlink of the space based system,and receives at frequencies within the first frequency band used as thedownlink of the space based system.

The first and second frequencies used by a cell of the space basedsystem are optionally mutually exclusive to third frequencies used by acell of the ground based system containing one or more of the subscriberterminals, within the cell of said space based system.

The means for determining available communication links comprises firstand second means for determining available communication links, whereina first means for determining available communication links is utilizedin connection with the ground based system, and wherein a second meansfor determining available communication links is utilized in connectionwith the space based system.

The system further optionally comprises means for maintaining cognizanceof the availability of at least one of satellite and terrestrialresources and administering reconfiguration, assignment and/or reuse offrequencies within the predetermined frequency band to meet changedtraffic patterns or other predetermined conditions. The means formaintaining cognizance is optionally operatively connected to at least aMSC that assigns a channel to subscriber units.

In another embodiment, a cellular communications system in accordancewith the present invention comprises a space based system comprisingmeans for establishing a first set of cells and transmitting andreceiving GSM based waveforms using at least a first portion of at leastone predetermined frequency band used by the first set of cells. Aground based system comprises means for establishing a second set ofcells and transmitting and receiving code division multiple access(CDMA) waveforms utilizing at least a second portion of the onepredetermined frequency band to be used as at least one of an uplink anddownlink frequency channel from any of the frequencies within the atleast one predetermined frequency band. One or more subscriber terminalscommunicate with at least one of the space based system and with theground based system when located in at least one of the first and secondset of cells. The system also comprise means for determining availablecommunication links between the subscriber terminals and the space basedsystem and/or the ground based system.

The first portion of the at least one predetermined frequency bandoptionally comprises at least one discrete space based system uplinkportion and at least one discrete space based system downlink portion,wherein the first portion is a subset of the second portion. Each of thediscrete portions are optionally associated with at least one of asatellite spot beam and a subsection of a spot beam.

The first portion of the at least one predetermined frequency bandcomprises at least one discrete space based system uplink portion, atleast one discrete space based system downlink portion, and a groundbased system portion. At least two cells of the first set of cells inthe space based system optionally use a mutually exclusive portion ofthe first portion of the at least one predetermined frequency band.Further, one or more frequencies in the first and second portions of theat least one predetermined frequency band are optionally substantiallythe same or closely spaced.

The subscriber terminals optionally comprise a first vocoder having afirst data rate and a second vocoder having a second data rate, whereinthe first vocoder is used when the subscriber terminal is communicatingwith the space based system, and wherein the second vocoder is used whenthe subscriber terminal is communicating with the ground based system.

The means for determining available communication links furtheroptionally at least one of assigns and activates at least one of thefirst and second vocoders in response to predetermined criteria such ascapacity demand, voice quality, and/or received signal level.

The system further optionally comprises means for at least one ofassigning and activating a vocoder in response to predetermined criteriacomprising, for example, capacity demand, voice quality, and/or receivedsignal level.

The means for detecting available communication links optionally furtherassigns or activates a different vocoder to a voice communicationscircuit in response to the predetermined criteria such as capacitydemand, voice quality, signal strength, and received signal level havingchanged substantially since assignment or activation of the at leastfirst and second vocoder being utilized.

The system further optionally comprises means for maintaining cognizanceof the availability of at least one of satellite and terrestrialresources and administering reconfiguration, assignment and/or reuse offrequencies within the predetermined frequency band to meet changedtraffic patterns or other predetermined conditions. The means formaintaining cognizance is optionally operatively connected to at least amobile switching center that assigns a channel to subscriber units. Themeans for maintaining cognizance optionally utilizes hysteresis and/ornegative hysteresis in the reconfiguration, assignment and/or reuse ofthe frequencies.

There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described hereinafterand which will form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of description and should not beregarded as limiting.

As such, those skilled in the art will appreciate that the conception,upon which this disclosure is based, may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

Further, the purpose of the foregoing abstract is to enable the U.S.Patent and Trademark Office and the public generally, and especially thescientists, engineers and practitioners in the art who are not familiarwith patent or legal terms or phraseology, to determine quickly from acursory inspection the nature and essence of the technical disclosure ofthe application. The abstract is neither intended to define theinvention of the application, which is measured by the claims, nor is itintended to be limiting as to the scope of the invention in any way.

These together with other objects of the invention, along with thevarious features of novelty which characterize the invention, arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and the specific objects attained by its uses,reference should be made to the accompanying drawings and descriptivematter in which there is illustrated preferred embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art diagram of a satellite radiotelephone system;

FIGS. 2A, 2B and 2C are prior art schematic diagrams of frequency reusein the satellite radiotelephone system shown in FIG. 1;

FIG. 3 is a diagram showing an overview of the principal elements of aprior art communications system;

FIG. 4 is an overview block diagram of another embodiment of the priorart communications system shown in FIG. 3;

FIG. 5 is an exemplary high level block diagram of a system that can useand/or be used to produce the frequency reuse schemes in accordance withthe present invention;

FIG. 6 a is an exemplary illustration of how a base transceiver stationcan enhance network coverage, particularly in an area having no line ofsight path (or reduced line of sight path) with a satellite;

FIG. 6 b shows, for an embodiment of the present invention using asingle satellite, exemplary satellite uplink and downlink frequencybands commonly used by and shared with the terrestrial system;

FIG. 6 c shows, for an embodiment of the present invention using two ormore satellites, exemplary satellite uplink and downlink frequency bandscommonly used by and shared with the terrestrial system;

FIG. 6 d shows, for an embodiment of the present invention using asingle satellite, exemplary satellite uplink and downlink frequencybands;

FIG. 6 e shows, for an embodiment of the present invention using two ormore satellites, exemplary satellite uplink and downlink frequencybands;

FIG. 6 f shows two frequency bands, each having channels that can beutilized by the satellite and/or terrestrial components;

FIG. 6 g shows a single frequency band with channels that can beutilized by the satellite and/or terrestrial components;

FIG. 7 a is an exemplary high level block diagram illustrating anintegrated satellite-terrestrial system that can use and/or be used, forexample, to produce the frequency reuse schemes in accordance with thepresent invention;

FIG. 7 b is an exemplary high level block diagram illustrating anintegrated satellite-terrestrial system, utilizing a radio resourcemanager, that can use and/or be used, for example, to produce thefrequency reuse schemes in accordance with the present invention;

FIG. 7 c is an exemplary high level block diagram illustrating asatellite-terrestrial system having autonomous satellite and terrestrialcomponents that can use and/or be used, for example, to produce thefrequency reuse schemes in accordance with the present invention;

FIGS. 8 a, 8 b, 8 c and 8 d show exemplary embodiments of the presentinvention pertaining to how uplink and downlink frequencies can beutilized in the satellite and terrestrial components;

FIG. 9 is an exemplary schematic showing how link margins can beaffected when utilizing different air interfaces for the satellite andterrestrial components;

FIG. 10 shows an exemplary seven cell satellite spot beam pattern thatcan be used in connection with the present invention;

FIG. 11 is an exemplary schematic showing how terrain blockage canaffect assignment of frequencies;

FIG. 12 a shows an exemplary flow diagram of an overall system method,including assignment and reuse of channels based on signal strength, inaccordance with the present invention;

FIG. 12 b shows an exemplary flow diagram of a second overall systemmethod, including assignment and reuse of channels based on signalstrength, in accordance with the present invention;

FIG. 13 is a high level flow diagram illustrating the static and dynamicchannel assignment features of the present invention;

FIG. 14 shows an exemplary flow diagram of call initialization whenterrestrial mode is preferred while using common or partiallyoverlapping frequency bands as shown, for example, in FIGS. 6 b, 6 c, 6f and 6 g;

FIG. 15 shows an exemplary flow diagram of call initialization whenterrestrial mode is preferred while using discrete satellite andterrestrial frequency bands as shown, for example, in FIGS. 6 d and 6 e;

FIG. 16 shows an exemplary flow diagram of base station-to-base stationor base station-to-satellite handoff while using common or partiallyoverlapping frequency bands as shown, for example, in FIGS. 6 b and 6 c;

FIG. 17 shows an exemplary flow diagram of base station-to-base stationor base station-to-satellite handoff while using discrete satellite andterrestrial frequency bands as shown, for example, in FIGS. 6 d and 6 e;

FIG. 18 shows an exemplary method of satellite-to-base station orsatellite-to-satellite handoff while using common or partiallyoverlapping frequency bands as shown, for example, in FIGS. 6 b and 6 c;

FIG. 19 shows an exemplary method of satellite-to-base station orsatellite-to-satellite handoff while using discrete satellite andterrestrial frequency bands as shown, for example, in FIGS. 6 d and 6 e;and

FIGS. 20 a and 20 b, taken together, show an exemplary method of inverseassignment of the channels.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 5 shows an exemplary high level block diagram of a standard system500 that can be used to implement the frequency assignment, reuse and/orreassignment, and other features of the present invention. Thetelemetry, tracking and command (TT&C) facility 502 is used to controland monitor the one or more satellites 516 of the system 500.

The terrestrial segment can use digital cellular technology, consistingof or including one or more Gateway Station Systems (GSS) 504, a NetworkOperations Center (NOC) 506, one or more Mobile Switching Centers (MSC)508, one or more Base Transceiver Stations (BTS) 514, and a variety ofmobile, portable, Personal Digital Assistant (PDA), computer and/orfixed subscriber terminals 512. The subscriber terminals 512 can beequipped with a Subscriber Identity Module (SIM) (not shown) or similarmodule that identifies the individual subscriber terminal 512. Thesubscriber terminals 512 are generally handheld devices that providevoice, video and/or data communication capability. Subscriber terminals512 may also have additional capabilities and functionality such as, forexample, paging. Equipping the subscriber terminals 512 with a SIMmodule can allow the user to have access to the system 500 by using anysubscriber terminals 512 having an authorized SIM.

The MSC 508 preferably performs the switching functions of the system500, and also optionally provides connection to other networks (e.g.,Public Data Network (PDN) 517, and/or Public Switched Telephone Network(PSTN) 518). Since the subscriber terminals 512 do not know whatchannels are actually being used by the satellite and/or terrestrialsystem, the MSC 508 in accordance with at least one embodiment of thepresent invention optionally identifies the channels that are in use andthe channels that are not in use. In another embodiment, the MSC 508 canreceive updates from each terrestrial and satellite control center andor one or more radio resource managers (RRM) regarding is which channelsare in use. The MSC 508 is preferably connected to a BSC 510 which, inturn, is preferably connected to a BTS 514. Therefore, in at least oneembodiment of the present invention, the MSC 508, via one or more RRMs,determines which channels are in use or not in use.

Subscriber terminals 512 are preferably providing signal strengthmeasurements and/or other measurements such as interference level, ofthe satellites 516 to, for example, a BTS 514. It is preferred that theBSC 510 assign a channel to the subscriber terminal 512. It is alsopreferred that the BSC 510 first assign to the subscriber terminal 512 achannel that is not in use by the satellite. If all of the channels arein use, then the BSC 510 selects, for example, the satellite channelhaving the weakest signal strength relative to the subscriber terminal512. Alternatively, any standard algorithm can optionally be used todetermine a preferred channel to use.

BTSs 514 can be used in those areas where the satellite signal isattenuated by, for example, terrain and/or morphological features,and/or to provide in-building coverage. The BTSs 514 and BSCs 510generally provide and control the air interface to the subscriberterminals 512. The BTSs 514 can optionally use any standard wirelessprotocol that is very similar to that of the satellites 516.Alternatively, BTSs 514 can use a first air interface (e.g., CDMA), andthe satellite 516 can use a second air interface (e.g., GSM, or GlobalMobile Satellite Systems (GMSS), which is a satellite air interfacestandard which is developed from GSM). The BSC 510 generally controlsone or more BTSs 514 and manages their radio resources. BSC 510 isprincipally in charge of handovers, frequency hopping, exchangefunctions and control of the radio frequency power levels of the BTSs514.

NOC 506 can provide functions such as, for example, monitoring of systempower levels to ensure that transmission levels remain withintolerances, and line monitoring to ensure the continuity of thetransmission lines that interconnect the BSC 510 to the BTS 514, thatinterconnect the MSC 508 to the PDN 517 and that interconnect the PSTN518, and the NOC 506 to other network components. The NOC 506 can alsomonitor the satellite 516 transponders to ensure that they aremaintained within frequency assignment and power allocation tolerances.The NOC 506 also ensures that communication resources are availableand/or assigned, reused and/or borrowed in a timely manner to, forexample, facilitate calls originating and/or transmitted to a subscriberterminal 512. Finally, to effectuate, for example, the dynamic channelassignment of the present invention, the NOC 506 generally maintainscognizance of the availability of satellite and/or terrestrial resourcesand arranges for any necessary satellite reconfiguration and/orassignment and or reuse of frequencies to meet changed traffic patterns.An exemplary NOC is described in U.S. Pat. No. 5,926,745, incorporatedherein by reference.

The system 500 will also have one or more satellites 516 thatcommunicate with the GSS 504 and the subscriber terminals 512. A typicalGSS 504 will have an antenna to access the satellite 516. On the uplinktransmission path, the GSS 504 will generally have upconverters that cantranslate the GSS 504 intermediate frequency (IF) to the feeder linkfrequency. On the downlink transmission path, the received signal ispreferably amplified, and feeder link frequencies are translated to thecommon IF.

The system 500 generally comprises satellite and terrestrial components.Satellite components comprise, for example, TT&C 502, GSS 504, andsatellite 516. Terrestrial components comprise, for example, BSC 510 andBTSs 514. In the FIG. 5 embodiment, the NOC 506, MSC 508 are shared bythe satellite and terrestrial systems. As will be discussed with regardto FIGS. 7 a-7 d, alternate embodiments of the present inventionprovide, for example, separate NOCs 506 and/or MSCs 508 for thesatellite and terrestrial components to facilitate autonomous orsubstantially autonomous operation.

FIG. 6 a is an exemplary BTS 514 frequency plan. The nomenclature isprovided as follows:

-   -   f^(U) _(1a) and f^(D) _(1a)    -   superscripts U and D indicate uplink and downlink, respectively;    -   the numeric subscript (e.g., 1) indicates the frequency band;        and    -   the letter subscript (e.g., a) indicates the channel within the        frequency band.

Users communicating on uplink 604 and downlink 602 would use, forexample, paired uplink and downlink channels f^(U) _(1a) and f^(D)_(1a), f^(U) _(1b) and f^(D) _(1b), f^(U) _(1c) and f^(D) _(1c), etc.Advantageously, in the present invention, different channels within thesame frequency band, or different frequency bands, are optionallyassigned, reused and/or reassigned in a non-pairwise manner. Forexample, downlink 602 could be using f^(D) _(1a), whereas uplink 604could be using f^(U) _(1b). Similarly, downlink 602 could be using f^(D)_(1c) whereas uplink 604 could be using f^(U) _(1d). These pairings areillustrative only, insofar as numerous other non-pairwise uplink 604 anddownlink 602 combinations are available that can be used, for example,within different terrestrial cells, within different areas of a spotbeam, and/or between different spot beams.

Further, suppose that f^(U) _(2a) and f^(D) _(2a) are the uplink anddownlink frequency bands associated with a second domestic or foreignsatellite system. Users of system 500 communicating on downlink 602 anduplink 604 could use, for example, uplink and downlink frequencies f^(U)_(3a) and f^(D) _(2a), F^(U) _(1c) and f^(D) _(2b), f^(U) _(1b) andf^(D) _(2c), etc. In general, the present invention optionally uses oneor more uplink and downlink channels that are from different frequencybands and/or associated with a different domestic and/or foreignsatellite system.

FIG. 6 b shows, for a single satellite system, illustrative uplink 604and downlink 602 frequencies/channels that can be used with thesatellite component. Each channel generally comprises a control portionand a data or voice portion. As shown, and as will be discussed in moredetail with regard to FIGS. 8 a-8 c, the satellite uplink 604 anddownlink 602 frequencies, in accordance with at least one embodiment ofthe present invention, are commonly used and shared by the terrestrialcomponent, and generally comprise a range of separated frequencies(e.g., 1626.5-1660.5 MHz for uplink, and 1525-1559 MHz for downlink).The present invention is not limited, however, to sharing frequencieswithin a single frequency band assigned and/or designated by, forexample, a government regulatory agency. The present system may alsotherefore, share and/or reuse frequencies of other domestic, foreign,and/or international satellite and/or terrestrial systems, subject to,for example, national, foreign, and/or international governmentregulatory approval.

Accordingly, as defined in connection with the present invention, afrequency band comprises any set of frequencies, and is not limited to aconsecutive set or series of frequencies. Further, a frequency band inalternative embodiments may comprise a logical set of frequencies thatmay be assigned to different communication systems, carriers, or inother predesignated frequency bands. That is, for example, a frequencyband in the present invention may include frequencies that are assignedto other frequency bands, for example, for different purposes. Withregard to FIG. 6 b, individual channels 603, 605 are shown withinfrequency bands 604, 602, respectively.

FIG. 6 c shows, for a multiple satellite system, illustrative uplinks604 a, 604 b and downlinks 602 a, 602 b within the frequency bands ofthe satellite system. FIG. 6 c can equally be used to provide differentfrequency bands associated with various spot beams of a singlesatellite, and/or subparts or subsectors of a single spot beam. Asshown, the satellite uplink 604 a, 604 b and downlink 602 a, 602 bfrequencies, in accordance with at least one embodiment of the presentinvention, are commonly used and shared by the terrestrial system, andgenerally comprise a range of separated frequencies (e.g., 1626.5-1643MHz for satellite 1 uplink 604 a, 1644-1660.5 MHz for satellite n uplink604 n, and 1525-1542 MHz for satellite 1 downlink 602 a, and 1543-1559MHz for satellite n downlink 602 n). Individual channels 607, 609 areshown within uplink frequency bands 604 a, 604 b, respectively, andindividual channels 611, 613 are shown within downlink frequency bands602 a, 602 b, respectively.

FIG. 6 d shows an alternate embodiment of the frequency bands of FIG. 6b in which the satellite frequencies 602 c, 604 c and the terrestrialfrequencies 602 d, 604 d are discrete. That is, in contrast to thefrequency bands shown in FIG. 6 b, where satellite and terrestrialfrequencies comprise common frequency bands 602, 604, in FIG. 6 d thereis no sharing of satellite and terrestrial frequencies within a commonfrequency band. Individual channels 611, 613, 615, and 617, are shownwithin frequency bands 602 c, 602 d, 604 c, and 604 d, respectively.

FIG. 6 e shows an alternate embodiment of the frequency bands of FIG. 6c in which the satellite-frequencies 602 e, 602 f, 604 e, 604 f andterrestrial frequencies 602 g, 604 g are discrete. That is, in contrastto the frequency bands shown in FIG. 6 c, where satellite andterrestrial frequencies comprise common frequency bands 602 a, 602 b,604 a, 604 b, in FIG. 6 e there is no sharing of satellite andterrestrial frequencies within a common frequency band. Individualchannels 619, 621, 623, 625, 627, and 629 are shown within frequencyhands 602 e, 602 f, 602 g, 604 e, 604 f and 604 g, respectively. FIG. 6e can equally be used to provide different frequency bands associatedwith various spot beams of a single satellite, and/or subparts orsubsectors of a single spot beam.

FIG. 6 f shows an alternate embodiment of the frequency bands of FIG. 6b. In FIG. 6 f, frequency bands 606 a, 606 b each contain channels thatcan be used for satellite uplink, satellite downlink and/orterrestrially. FIG. 6 g shows a single frequency band 608 that containschannels that can be used for satellite uplink, satellite downlinkand/or terrestrially.

FIG. 7 a is an exemplary high level block diagram of asatellite-terrestrial system that can use, for example, the frequencyassignment and/or reuse schemes in accordance with the presentinvention. The system of FIG. 7 a is at least partially integrated inthat the satellite component and the terrestrial component each share acommon NOC 506 and MSC 508 (wherein S-MSC represents the satelliteportion of the MSC 508, and T-MSC represents the terrestrial portion ofthe MSC).

Although FIG. 7 a illustrates a GSM architecture, the satellite andterrestrial components comprising the system 500 of the presentinvention are not limited to the use of a GSM system, and can bedeployed with all satellite (e.g., LEO, MEO, GEO, etc.) and cellularterrestrial technologies (e.g., TD, CDMA, GSM, etc., or any combinationsthereof).

An exemplary Home Location Register (HLR) 706 comprises a database thatstores information pertaining to the subscribers belonging to the system500. The HLR 706 also stores the current location of these subscribersand the services to which they have access. In an exemplary embodiment,the location of the subscriber corresponds to the SS7 504 address of theVisitor Location Register (VLR) 702 associated with the subscriberterminal 512.

An exemplary VLR 702 contains information from a subscriber's HLR 706 inorder to provide the subscribed services to visiting users. When asubscriber enters the covering area of a new MSC 508, the VLR 702associated with this MSC 508 will request information about the newsubscriber to its corresponding HLR 706. The VLR 702 will then haveenough information in order to administer the subscribed serviceswithout needing to ask the HLR 706 each time a communication isestablished. The VLR 702 is optionally implemented together with a MSC508, so the area under control of the MSC 508 is also the area undercontrol of the VLR 702.

The Authentication Center (AUC) 708 register is used for securitypurposes, and generally provides the parameters needed forauthentication and encryption functions. These parameters help to verifythe user's identity.

In accordance with the present invention, and as disclosed in U.S. Pat.No. 5,812,968, which in incorporated herein by reference, a subscriberterminal 512 can optionally utilize a standard variable rate vocoder(i.e., a voice encoder that at two or more data rates codes/decodes, forexample, human speech into/from digital transmission) or multiplevocoders, each transmitting at a different data rate to, for example,increase effective system 500 bandwidth, voice or data quality, receivedsignal level, and/or link margin. As used herein, link margin is definedas the difference between the signal-to-noise ratio available to thereceiver (e.g., subscriber terminal 512, BTS 514 and/or satellite 516)and the signal-to-noise ratio needed at the receiver to achieve aspecific performance (e.g., Bit Error Rate (BER)).

For example, one or more of the subscriber terminals 512 can have avariable rate vocoder used for both satellite and terrestrialcommunication having data rates of, for example, 13.0 kbit/sec, 6.0kbit/sec, 3.6 kbit/sec, 2.4 kbit/sec, and 2.0 kbit/sec. Alternatively,one or more of the subscriber terminals 512 can have, for example, avariable rate vocoder for terrestrial communications, and a variablerate vocoder for satellite communications. One or more of the subscriberterminals 512 could also have a plurality of vocoders having differentdata rates and used for terrestrial communication, and a plurality ofvocoders having different data rates and used for satellitecommunication. The MSC 508 and/or the GSS 504 and BSC 510, for example,can also utilize corresponding vocoders to coordinate data rateselection and/or transition.

If the system 500 determines that system 500 channel usage, or channelusage within a portion of the system 500, is reaching a predeterminedthreshold (e.g., 90%), a control signal can be transmitted to one ormore subscriber terminals 512 directing usage of a lower vocoder datarate. Thus if the subscriber terminal 512 was utilizing, for example, avocoder having a 13.0 kbit/sec data rate, the subscriber terminal 512could now be directed to utilize, for example, a vocoder having a 2.4kbit/sec data rate, thereby increasing the effective bandwidth of thesystem 500 (by permitting additional calls). Use of a higher data ratecan optionally resume when channel usage falls below a predeterminedthreshold (e.g., 60%).

Similarly, if the system 500 determines that the BER exceeds apredetermined threshold (e.g., 10⁻³ for voice), the system 500 cantransmit a control signal to one or more subscriber terminals 512directing usage of a lower vocoder data rate. Thus if the subscriberterminal 512 was utilizing a vocoder having a 13.0 kbit/sec data rate,the subscriber terminal 512 could now be directed to utilize a vocoderhaving, for example, a 2.4 kbit/sec data rate, thereby reducing the biterror rate by effectively increasing the available link margin. Use of ahigher vocoder rate can optionally resume when voice quality and/or linkmargin exceeds a predetermined threshold.

Specifically, the satellite 516 or a BSC 510 could send a control signalto, for example, the subscriber terminal 512, optionally via MSC 508,indicating whether the signals received from the subscriber terminal 512are of a sufficient quality. For example, a GSM-based Fast AssociatedControl Channel (FACCH) signal, which is used for time criticalsignaling such as when performing handovers, can be sent to a subscriberterminal 512 to indicate that the signals received are not of sufficientquality. A receiver unit (not shown), for example, within the subscriberterminal 512 can in turn send a control signal to, for example, avariable rate vocoder within the subscriber terminal 512 to cause thevocoder to reduce the bit rate of the signal being transmitted from thesubscriber terminal 512 to the satellite 516.

Finally, the variable rate vocoder can be used to improve the effectivereceived signal level as determined by, for example, received signalstrength indication (RSSI), which is the measured power of a receivedsignal. The RSSI is a relative measure of received signal strength for aparticular subscriber terminal 512, and can optionally be based on, forexample, automatic gain control settings. If the system 500 determinesthat the RSSI is below a predetermined threshold, the MSC 508, forexample, can transmit a control signal to one or more subscriberterminals 512 to utilize a lower vocoder data rate. Thus, if one or moreof the subscriber terminals 512 was utilizing a data rate of 13.0kbit/sec, the subscriber terminal(s) 512 could now utilize a data rateof 2.4 kbit/sec, thereby increasing the effective link margin.

FIG. 7 b is an exemplary high level block diagram illustrating anotherembodiment of the satellite-terrestrial system that utilizes a radioresource manager (RRM) 720. The RRM 720 is preferably communicable withGSS 504, with the BSCs 510 (not shown), with the MSC 508, and/or withone or more BTSs 514. The RRM 720 is preferably used to determinechannels currently in use, and to optionally monitor inband interferenceto avoid, for example, using channels expected to cause unacceptablelevels of interference (e.g., a level of interference exceeding apredetermined threshold as defined, for example, by BER). The RRM 720can also optionally be used to monitor received signal quality andavailable link margin, and execute, for example, an intra-beam and/orintra-band hand-over of the communications channel when a qualitymeasure thereof has fallen below a predetermined level and/or hasexhausted a predetermined amount of link margin.

The RRM 720 preferably has means for determining which channels arebeing used by the system 500. For example, RRM 720 can comprise orutilize, for example, a suitable antenna operatively connected to aspectrum analyzer capable of searching, for example, one or morefrequency bands for the presence of radio signals, and to determine whatchannels are currently being utilized within the frequency band(s).Thus, by being able to monitor usage of one or more of the frequencybands shown, for example, in FIGS. 6 b-6 e, the RRM 720 can identify allof the channels allocated to the system 500 that are currently beingused. Alternatively, the system 500, via direct connection can informthe RRM 720 as to what channels are in use. In this embodiment, the RRM720 does not need to monitor whether the channels are being used byeither the satellite or terrestrial component(s); the RRM 720 simplydetermines whether a channel is currently in use or not in use.

As discussed with regard to the embodiment of the present inventionshown in FIG. 7 a, the subscriber terminals 512 of the embodiment shownin FIG. 7 b can also utilize a variable rate vocoder or multiplevocoders, each transmitting at a different data rate to, for example,increase effective system 500 bandwidth, voice quality, effectivereceived signal level, and/or link margin. The MSC 508 and/or the GSS504 and BSC 510 (not shown), for example, can also utilize correspondingvocoders to coordinate data rate selection and/or transition.

If the system 500 determines that system channel usage, or channel usagewithin a portion of the system 500, is reaching a predeterminedthreshold (e.g., 90%), a control signal can be transmitted to one ormore subscriber terminals 512 directing usage of a lower vocoder rate.Thus if the subscriber terminal 512 was utilizing a vocoder having a13.0 kbit/sec data rate, the subscriber terminal 512 could now bedirected to utilize, for example, a vocoder having a 2.4 kbit/sec datarate, thereby increasing the effective bandwidth of the system 500 (bypermitting additional calls utilizing a lower data rate). Use of ahigher data rate can optionally resume when channel usage falls below apredetermined threshold (e.g., 60%).

Similarly, if the system 500 determines that voice quality as determinedby, for example, bit error rate exceeds a predetermined threshold (e.g.,10⁻³ for voice), the system 500 can transmit a control signal to one ormore subscriber terminals 512 directing usage of a lower vocoder datarate. Thus, if a subscriber terminal 512 was utilizing a vocoder havinga 13.0 kbit/sec data rate, the subscriber terminal 512 could now bedirected to utilize a vocoder having a 2.4 kbit/sec data rate, therebyreducing the bit error rate. Use of a higher vocoder rate can optionallyresume when voice or data quality exceeds a predetermined threshold.

Specifically, the satellite 516 or a BSC 510 (not shown), for example,can send a signal to a subscriber terminal 512, via MSC 508, indicatingwhether the signals received from the subscriber terminal 512 are of asufficient quality. For example, a GSM-based FACCH signal, as previouslydiscussed, can be sent to a subscriber terminal 512 to indicate that thesignals received are not of sufficient quality. A receiver unit (notshown), for example, within a subscriber terminal 512 can in turn send acontrol signal to, for example, a variable rate vocoder within thesubscriber terminal 512 to cause the vocoder to reduce the bit rate ofthe signal being transmitted from the subscriber terminal 512 to thesatellite 516.

Finally, the variable rate vocoder can be used to improve effectivereceived signal level as determined by, for example, RSSI. In this case,if the system 500 determines that the RSSI is below a predeterminedthreshold, the MSC 508, for example, can transmit a control signal toone or more subscriber terminals 512 to utilize a lower vocoder datarate. Thus if the subscriber terminal 512 was utilizing a data rate of13.0 kbit/sec, the subscriber terminal 512 could now utilize a data rateof 2.4 kbit/sec, thereby increasing effective RSSI and/or link margin.

FIG. 7 c is an exemplary high level block diagram illustrating anotherembodiment of an autonomous satellite-terrestrial system in accordancewith the present invention. In this embodiment, the satellite andterrestrial components each have their own RRMs 720 a and 720 b, MSCs508 a, 508 h, and NOCs 506 a, 506 b, respectively. As shown, thesatellite and terrestrial components also have their own respective VLRs702 a, 702 b, HLRs 706 a, 706 b, and AUCs 718 a, 718 b. In alternateembodiments, the VLRs 702 a, 702 b, HLRs 706 a, 706 b, and/or AUCs 718a, 718 b can also be connected to, for example, the PSTN 518.

As discussed with regard to FIG. 5, the NOCs 506 a, 506 b ensure thatcommunication resources are available and/or assigned, reused and/orborrowed in a timely manner. Thus, by advantageously providing separateNOCs 506 a, 506 b, MSCs 508 a, 508 b, RRMs 720 a, 720 b, VLRs 702 a, 702b, HLRs 706 a, 706 b, and AUCs 718 a, 718 b in this embodiment, thesatellite and terrestrial components, while sharing and/or beingassigned to at least a portion of a common frequency band tan operateindependently of each other.

Since, as previously discussed, RRMs 720 a, 720 b can determine thechannels currently being utilized, RRM 720 b can therefore determine,independently and without communication with RRM 720 a or any othersatellite component equipment, what channels are not being used forsatellite communication by the system 500. For example, the RRMs 720 a,720 b can comprise or utilize, for example, a suitable antennaoperatively connected to a spectrum analyzer capable of searching a bandof radio frequencies for the presence of radio signals, to determinewhat frequencies are currently being utilized within a range or rangesof frequencies of interest. RRM 720 b can therefore determine,independently and without communication with RRM 720 a associated withthe satellite component, or any other satellite component equipment,what frequencies are not being used by the system for satellitecommunication. Since the RRM 720 b knows the frequencies used across arange of frequencies of interest, as well as the frequencies used by theterrestrial component, RRM 720 b can also determine or deduce thefrequencies that are currently being used by the satellite component.Similarly, the satellite component functions in substantially the samemanner to, inter alia, determine the frequencies currently being used bythe terrestrial component.

Similarly, RRM 720 a could also use, for example, an antenna incombination with frequency and/or spectrum analysis techniques todetermine, independently and without communication with RRM 720 b or anyother terrestrial component equipment, what channels are being used bythe system 500 for terrestrial communications. Since RRM 720 a knows allof the channels used across a range of frequencies of interest, as wellas the channels used by the satellite component, RRM 720 a can identifythe channels that are currently being used by the terrestrial component.

As discussed with regard to the embodiment of the present inventionshown in FIGS. 7 a and 7 b, the subscriber terminals 512 of theembodiment shown in FIG. 7 c can also utilize a variable rate vocoder ormultiple vocoders, each transmitting at a different data rate to, forexample, increase effective system 500 bandwidth, voice quality,received signal level, and/or link margin. The MSC 508 a, 508 b and/orthe GSS 504 and BSC 510 (not shown), for example, can also utilizecorresponding vocoders to coordinate data rate selection and/ortransition.

If the system 500 determines that system 500 channel usage, or channelusage within a portion of the system 500, is reaching a predeterminedthreshold (e.g., 90%), a control signal can be transmitted to one ormore subscriber terminals 512 directing usage of a lower vocoder datarate. Thus, if a subscriber terminal 512 was utilizing a vocoder havinga 13.0 kbit/sec data rate, the subscriber terminal 512 could nowutilize, for example, a vocoder having a 2.4 kbit/sec data rate, therebyincreasing the effective bandwidth of the system 500 (by permittingadditional calls utilizing a lower data rate). Use of a higher data ratecan optionally resume when channel usage falls below a predeterminedthreshold (e.g., 60%).

Similarly, if the system 500 determines that voice or data quality asdetermined by, for example, bit error rate exceeds a predeterminedthreshold (e.g., 10⁻³ for voice), the system 500 can transmit a controlsignal to one or more subscriber terminals 512 directing usage of alower vocoder data rate. Thus, if a subscriber terminal 512 wasutilizing a vocoder having a 13.0 kbit/sec data rate, the subscriberterminal 512 could now be directed to utilize a vocoder having a 2.4kbit/sec data rate, thereby reducing the bit error rate. Use of a highervocoder rate can optionally resume when voice quality exceeds apredetermined threshold.

Specifically, the satellite 516 or a BSC 510 (not shown) can send asignal to the subscriber terminal 512, via MSC 508 a or MSC 508 b,respectively, indicating whether the signals received from thesubscriber terminal 512 are of a sufficient quality. For example, aGSM-based FACCH signal, as previously discussed, can be sent to asubscriber terminal 512 to indicate that the signals received are not ofsufficient quality. A receiver unit (not shown), for example, within thesubscriber terminal 512 can in turn send a control signal to, forexample, a variable rate vocoder within the subscriber terminal 512 tocause the vocoder to reduce the bit rate of the signal being transmittedfrom the subscriber terminal 512 to the satellite 516 or to the BTS 514

Finally, the variable rate vocoder can be used to improve receivedsignal level as determined by, for example, RSSI. In this case, if thesystem 500 determines that the RSSI is below a predetermined threshold,the respective MSC 508 a, 508 b, for example, can transmit a controlsignal to one or more subscriber terminals 512 to utilize a lowervocoder data rate. Thus, if a subscriber terminal 512 was utilizing adata rate of 13.0 kbit/sec, the subscriber terminal 512 could nowutilize a data rate of 2.4 kbit/sec, thereby increasing the effectiveRSSI and/or link margin.

FIGS. 8 a, 8 b, and 8 c show exemplary embodiments of the presentinvention pertaining to how uplink and downlink frequencies can beutilized in or by the satellite and terrestrial components, FIG. 8 ashows a first exemplary embodiment where the satellite 516 downlink f₁is used, assigned and/or reused as the terrestrial downlink f₁.Similarly, the satellite uplink f₁ is used as the terrestrial uplinklink f₂. Interference with channels typically may result when, forexample, a subscriber terminal 512 has a direct line of sight path toone or more satellites, and also has a communication link with aterrestrial BTS having the same or nearby frequency.

The embodiment shown in FIG. 8 b involves reversing the satellitedownlink f₁ and satellite uplink f₂ frequencies to become theterrestrial uplink link f₁ and terrestrial downlink link f₁ frequencies,respectively. As a result, there will be two possible interferencepaths: (1) between the satellite 516 and BTS 514, as uplink to downlinkinterference on f₁, and as uplink to downlink interference on f₂, and(2) between the satellite subscriber terminals 512 a and terrestrialsubscriber terminals 512 b, as downlink to uplink interference on f₁,and as downlink to uplink interference on f₂. Measures should be takento eliminate or substantially reduces both of these possibleinterferences.

For example, to minimize these interferences, BTSs 514 that have asubstantially reduced gain in the geostationary arc (i.e., the elevationangle above the horizon from a base station to the satellite) can beutilized. Within North America, the geostationary arc typically variesfrom approximately 30° to 70°, depending, for example, on the latitudeof the base station. To fully take advantage of this fact, it ispreferred that the base station antenna pattern have a null, andtherefore significantly reduced gain, in the geostationary arc portionof its vertical pattern.

In addition, it is preferred that the BTSs 514 be optimally orsubstantially optimally located and oriented to advantageously utilizethe horizontal gain pattern of the antenna. The benefits of using thistechnique, for example, are that frequency reuse will be maximized orsubstantially maximized, thereby enhancing the overall capacity of thesystem, and further reducing or eliminating interference.

In addition to the increased isolation provided by the vertical antennapattern, additional isolation can be obtained from the horizontalantenna pattern. For example, preferably by configuring BTSs 514 suchthat the azimuth to the satellite is off-bore or between sectors,several additional dB of isolation can typically be achieved. By keepingthis configuration standard for, say, a cluster of base stations,frequency reuse for the terrestrial system can generally be increased.

Interference between satellite subscriber terminals 512 a andterrestrial subscriber terminals 512 b is typically a problem when theunits are in relatively close proximity to one another. It is preferredthat such interference be substantially reduced or eliminated by, forexample, first detecting close proximity before the assignment of aradio channel (i.e., during call initialization), and secondly byproviding a hand-off to a non-interfering channel if close proximityoccurs after the assignment of a radio channel. For example, arelatively small group of channels, called “transition channels”, can bereserved for single-mode terminals. The single mode terminals preferablyuse transition channels while inside base station coverage. It is alsopreferred that dual-mode terminals also use the transition channelsunder certain circumstances. For example, after a dual mode terminalscans channels for signal strength and interference, a transitionchannel can be utilized if unacceptable levels of interference aredetected.

The embodiment shown in FIG. 8 c involves using the satellite systemuplink f₂ as both the terrestrial system downlink f₂ and uplink f₂frequencies using time division duplex techniques. In alternateembodiments, the terrestrial downlink and uplink frequencies areoptionally discrete bands. For example, downlink frequencies maycomprise f_(2a), and uplink frequencies may comprise f_(2b).

Finally, the embodiment shown in FIG. 8 d involves using the satellitesystem downlink f₁ as both the terrestrial system downlink f₁ and uplinkf₁ frequencies using time division duplex techniques. In alternateembodiments, the terrestrial downlink and uplink frequencies areoptionally discrete bands. For example, downlink frequencies maycomprise f_(1a), and uplink frequencies may comprise f_(1b).

FIG. 9 is an exemplary schematic showing how link margins can beaffected when the satellite and terrestrial components use different airinterfaces simultaneously in overlapping areas of coverage. FIG. 9assumes that the satellite component uses GSM 902, and that theterrestrial component uses CDMA 904. However, the principles discussedherein with regard to FIG. 9 are generally applicable to any airinterface(s) that may be used with the satellite and terrestrialcomponents.

As shown, the GSM channel 902 can be a 200 kHz channel, and the CDMAchannel 904 can be a 1.25 MHz channel. If the satellite component isusing the GSM channel 902 and the terrestrial component is not operating(i.e., the 1.25 CDMA channel is not being used), there will be a noisefloor A, and the subscriber terminals 512 will provide output at powerlevel 910. The link margin can be increased by, for example, increasingpower output level 910, reducing noise floor A, or a combinationthereof.

When the terrestrial system goes into use, the noise floor is indicatedby C, which generally corresponds to the aggregate power output of theCDMA channel 904. In order to compensate for the increased noise floor Cand increase their link margin, subscriber terminals 512 operating inthe GSM/satellite mode will provide output at power level 912 toovercome the higher noise floor C. Accordingly, subscriber terminalswill provide output at 912 to provide sufficient link margin.

Now, consider the situation in which subscriber terminals 512 are usingthe CDMA channel 904, but not the GSM channel 902. In such a case, theterrestrial component will generally be able to utilize all n CDMAchannels per carrier.

When the satellite component goes into use, subscriber terminals 512operating in the satellite mode will detect noise floor C, assuming thatsubscriber terminals 512 are utilizing all n CDMA channels. Accordingly,subscriber terminals 512 operating in the satellite mode will output atlevel 912, which appears as noise to the subscriber terminals 512operating in the terrestrial mode. The terrestrial system will thengracefully degrade by, for example, prohibiting, for a period of time,subscriber terminal 512 use of certain user codes n (e.g., channels)once the calls have, for example, been terminated. The RRM 720 (or 720a) can determine when additional calls can be established byconsidering, for example, anticipated link margin on the call to beestablished.

FIG. 10 shows a single satellite 516 providing a first set of cells 1-7in the form of a seven cell pattern. A second set of terrestrial cells8-10 is also shown, each generally comprising or operationallycommunicable with a BTS 514. FIG. 10 can use any of the embodimentsdiscussed with regard to FIGS. 7 a-7 d. Multiple satellites and/or anynumber of cells and/or cell configurations may be used.

Suppose a subscriber terminal 512 (not shown) positioned withinterrestrial cell 8 wishes to use a channel when all channels arecurrently being used by the satellite 516. If all channels are currentlybeing used (see, e.g., FIGS. 6 b-6 g), the subscriber terminal 512 willpreferably measure and select the satellite channel or channel that isbusy with the weakest signal strength to be reused terrestrially by thesubscriber terminal 512. Selecting the satellite channel with theweakest signal generally minimizes the interference between thesatellite 516 and the subscriber terminal 512.

Generally, the channels associated with the spot beam mostgeographically distant from the subscriber terminal 512 (in, forexample, terrestrial cell 8) have the weakest signal strength and thuswill cause the least interference. Thus, with regard to terrestrial cell8, the channels associated with cells 7 and 2 are the furthest distance(geographically), and will generally cause the least interference.Channels selected from cells 3 and 6 will generally cause moreinterference than those channels selected from cells 7 and 2, channelsselected from cells 5 and 4 will generally cause more interference thanchannels selected from cells 3 and 6, and channels selected from cell 1will generally cause the most interference. If there is an availablechannel that is not being used (by either the satellite or terrestrialcomponents), the subscriber terminal 512 is preferably assigned anunused channel. Once the call is setup, handover will be performed ifinterference levels having, for example, a predetermined threshold aredetected. The above process may alternatively or in addition be used forsystems with overlapping satellite-satellite coverage and/or overlappingterrestrial-terrestrial coverage.

As shown in FIG. 11, the present invention can also be practiced withtwo or more satellites 516 a, 516 b, each having their own respectivespot beam 1104 a, 1104 b. The (two or more) satellites 516 a, 516 b willgenerally have different assigned frequency bands and associatedchannels, as shown, for example, in FIG. 6 c. Each spot beam 1104 a,1104 b can further comprise, for example, two or more subareas orsubsectors, each having their own frequency band or portion thereofassociated therewith.

When possible, subscriber terminal 512 a (512 a, 512 b, 512 c, 512 d canrepresent a single terminal in four locations, or four differentsubscriber terminals) preferably measures signal strength of thesignaling and/or traffic channels associated with each satellite 516 a,516 b, and with at least the BTS 514 of the terrestrial cell (if any)that the subscriber terminal is positioned in. The signaling channelsare the control channels, and the traffic channels are where, forexample, voice conversations take place. For example, when thesubscriber terminal 512 a is positioned in terrestrial cell 1106, itwill measure the strength of signals from at least BTS 514 a. However,when the subscriber terminal 512 a is, for example, on a cell boundarybetween terrestrial cells 1106 and 1108, the subscriber terminal canoptionally measure the signal strength from, for example, BTS 514 a andBTS 514 b, and optionally from other neighboring BTS(s) (not shown). Itis preferred that subscriber terminals 512 continuously measure thesignal strength of the satellite 516 a, 516 b and the BTSs 514.

In general, when a channel is not in use by any communication systemcovering a predetermined area, the subscriber terminals 512 willpreferably and generally select for use the channel having the strongestsignal strength or other criteria that indicates a preferredcommunication channel such as band, capacity, protocols, time of day,location, interference level, and the link. With regard to FIGS. 6 b, 6c, 6 f and 6 g, any unused channel, however, can be selected toaccommodate, for example, network loading considerations. This channelcan be used to communicate with a subscriber terminal 512 either by thesatellite component (e.g., 602, 602 a, or 602 b) or terrestrialcomponent (e.g., 604, 604 a, or 604 b) of the system 500.

When all channels are in use, the subscriber terminal 512 willpreferably select a channel (e.g., 615) currently being used by thesatellite 516 having the weakest signal strength, and use that channelto communicate with a BTS 514 with which the subscriber terminal 512 hasthe strongest signal.

FIG. 12 a shows a first exemplary flow diagram of an overall systemmethod, including assignment and reuse of channels based, for example,on signal strength, in accordance with the present invention. FIG. 12 aassumes that there are separate satellite and terrestrial channels asshown, for example, in FIGS. 6 d and 6 e. At decision step 2 adetermination is made whether a terrestrial channel is available. Thedetermination can be made by a subscriber terminal 512, a RRM 720, 720a, 720 b, a BTS 514, or a NOC 508, 508 a, 508 b. For example, aspreviously described herein, the subscriber can select a channel basedon signal strength (and, for example, based on the channel having anacceptably low interference level and/or availability). Channelavailability as determined by the RRM 720, 720 a, 720 has been discussedwith regard to FIGS. 7 a-7 d. Similarly, as previously described herein,in at least one embodiment of the present invention, the BTS 514, viathe MSC 508 and the BSC 510, determines which channels are in use or notin use. NOCs(s) 508, 508 a, 508 b, can maintain cognizance of theavailability of satellite and/or terrestrial resources and/or arrangefor reconfiguration, assignment and/or reuse of frequencies to meetchanged traffic patterns.

If it is determined that a terrestrial channel is available, then anavailable channel is used terrestrially at step 20, and the processends. If a terrestrial channel is not available, a determination is madeat decision step 4 if a satellite channel is available. If so, anavailable channel is used for satellite communication at step 22, andthe process ends. If a satellite channel is not available, adetermination is made whether the one or more satellites are in ageosynchronous orbit at decision step 6.

If a geosynchronous orbit is utilized then, at decision step 8, adetermination is optionally made whether channels are dynamicallyassigned. If not, a predetermined satellite channel as determined by thesystem is reused terrestrially at step 10.

If a geosynchronous orbit is not utilized, or if a geosynchronous orbitwith dynamically assigned channels is utilized, or if the determinationregarding orbits is not made at all then, at decision step 14, adetermination is made whether the signal strength of the receivedsatellite channel(s) currently in use is too strong. If so, unacceptableinterference would occur between the satellite channel and that channelwhen it is reused terrestrially, and the process begins again atdecision step 2. If the signal strength of the received satellitechannel(s) is acceptably weak so as to not cause unacceptableinterference, a determination is made at decision step 16 whether thesignal strength is considered noise. If so, at step 12, any noisechannel can be selected for terrestrial reuse. If the satellite channelis not considered noise, then the non-noise satellite channel having theweakest signal strength is selected for terrestrial reuse.

FIG. 12 b shows a second exemplary flow diagram of an overall systemmethod, including assignment and reuse of channels based on signalstrength, in accordance with the present invention. FIG. 12 b assumesthat any channel can be used for satellite communication, terrestrialcommunication or, in the case of frequency reuse, simultaneous satelliteand terrestrial communication. FIGS. 6 f and 6 g show exemplaryfrequency band embodiments that can be used with the method inaccordance with FIG. 12 b.

At decision step 52 a determination is made whether a channel isavailable (i.e., not currently in use). As previously discussed withregard to FIG. 12 a, the determination can be made by a subscriberterminal 512, a RRM 720, 720 a, 720 h, a BTS 514, a MSC 508, or a NOC508, 508 a, 508 b. For example, as previously described herein, thesubscriber can select a channel based on signal strength (andavailability). Channel availability as determined by the RRM 720, 720 a,720 has been discussed with regard to FIGS. 7 a-7 d. Similarly, aspreviously described herein, in at least one embodiment of the presentinvention, the BTS 514, via the MSC 508 and the BSC 510, determineswhich channels are in use or not in use. NOCs(s) 508, 508 a, 508 b, canmaintain cognizance of the availability of satellite and/or terrestrialresources and/or arrange for reconfiguration, assignment and/or reuse offrequencies to meet changed traffic patterns.

If it is determined that a channel is available, a determination is madeat decision step 54 whether terrestrial coverage is available and, ifso, a channel is assigned for terrestrial use at step 72. If it isdetermined at decision step 4 that terrestrial coverage is notavailable, that at decision step 70, a determination is made whethersatellite coverage is available. If so, a channel is assigned forsatellite communication at step 74. If it is determined that satellitecoverage is not available, then the process returns to decision step 52.If at decision step 52 a determination is made that a channel is notavailable, then steps 56-78 are executed, as described with regard tosteps 6-18 of FIG. 12 a. It should be understood that criteria otherthan signal strength can be used in assigning channels, as will bediscussed, for example, with regard to FIG. 13.

Returning to FIG. 11, as discussed, when accessing (e.g., initiatingcommunication with) a channel, the subscriber terminal 512 a, ifpossible, determines the signal strength of the signaling channel(s)from the satellites) 516 a, 516 b, as well as the signaling channels ofat least BTS 514 a. In the case of subscriber terminal 512 a, terrainblockage 1102, for example, can affect assignment of frequencies sincesubscriber terminal 512 a can detect very little, if any, signal fromsatellite 516 a. It should be understood that assignment and/or reuse offrequencies can also be affected by, for example, man made structuresand/or naturally occurring phenomena such as foliage that can alsopartially or completely block or obstruct a line of sight between asubscriber terminal 512 a and a satellite 516 a, as well as by generalsignal attenuation.

When there is no direct line of site between subscriber terminal 512 aand satellite 516 a, little or no signal is “leaked” from the subscriberterminal 512 a to the satellite 516 a. At the same time, when there iscoverage from terrestrial BTS 514 a, the BTS 514 a can reuse a channelbeing used by satellite 516 a to communicate without interference, orsubstantially without interference, with subscriber terminal 512 a. Insuch a case, interference between the satellite 516 a and the subscriberterminal 512 a is minimized since, when signal attenuation occurs in thechannel from the subscriber terminal 512 a to the satellite 516 a, therealso is a substantially equal attenuation of the signal from thesatellite 516 a to the subscriber terminal 512 a. Therefore, if thesubscriber terminal 512 a detects a weak signal having, for example, apredetermined signal strength from a satellite 516 a, there will also bea correspondingly weak signal from the subscriber terminal 512 a to thesatellite 516 a. Thus, terrestrial reuse of a channel is preferred whenthe signal from the satellite 516 a to the subscriber terminal 512 a(and vice versa) is, for example, the weakest, or defined by, forexample, a predetermined signal quality (e.g., RSSI and/or bit errorrate).

In the embodiment shown in FIG. 7 d, the RRM 720 b, having determinedthe frequencies currently being used by the satellite component, canassign such channel for terrestrial reuse by a subscriber terminal 512.In general, it is preferred that the satellite having the channel withpredetermined criteria such as the weakest signal strength vis-à-vissubscriber terminal 512 a or other predetermined criteria is preferablyselected for terrestrial reuse.

Alternatively, if the subscriber terminal 512 a does not have coveragefrom a BTS 514, then terrestrial transmission cannot be utilized, andthe subscriber terminal 512 a preferably uses the satellite having thestrongest signal (which is satellite 516 b in this case).

Subscriber terminal 512 b has a direct line of sight to both satellites516 a, 516 b. Accordingly, the channel having the weakest signalstrength vis-à-vis subscriber terminal 512 b will preferably be selectedfor terrestrial reuse via, for example, BTS 514 b. As shown, althoughsubscriber terminal 512 c has a direct line of sight to satellite 516 a,the line of sight between subscriber terminal 512 c and satellite 516 bis blocked by terrain 1102. Accordingly, the signals received fromsatellite 516 b, assuming they can be received, by subscriber terminal512 c, will be weaker than the signals received by subscriber terminal512 c from satellite 516 a. Accordingly, the weakest channel fromsatellite 516 b will preferably be selected for terrestrial reuse bysubscriber terminal 512 c.

With regard to subscriber terminal 512 d, there is a line of sight toboth satellites 516 a, 516 b. In this case, an available (i.e., unused)channel having the strongest signal strength from either satellite 516a, 516 b is preferably selected for use since, as shown, subscriberterminal 512 d is not within a terrestrial cell (e.g., 1106, 1108) andis thus not covered (or sufficiently covered) by a BTS 514 to enableterrestrial communication.

Referring to FIG. 11, the present invention is also applicable to amobile satellite system (e.g., a Low Earth Orbit (LEO) system) or inwhich a given geographical area is covered on a dynamic basis by, forexample, two or more satellites. For example, in a mobile satellitesystem, at one point in time the spot beams of satellites 516 a, 516 bcould be 1104 a, 1104 b, respectively. At a subsequent (or previous)time, the satellite 516 a, 516 b, spot beams could cover an area asindicated by 1104 c, 1104 d, respectively.

In this scenario, a subscriber terminal 512 preferably recognizes, forexample, the signaling channels associated with each respective spotbeam 1104 a, 1104 b. In the case of overlapping coverage of spot beamswithin a given geographic area, the subscriber terminal 512 preferablymakes measurements on multiple signaling channels coming from multiplesatellites 516 a, 516 b. When all available channels are utilized or notavailable, subscriber terminal 512 preferably selects for reuse thechannel with the weakest signal strength in that given area. It shouldbe understood that although only two spot beams 1104 a, 1104 b(corresponding to satellites 516 a, 516 b, respectively) are shown, thesubscriber terminal 512 preferably measures the strength of, forexample, the signaling channels associated with any number of spotbeams/satellites.

When a subscriber terminal 512 is on the border or under the influence,for example, of two or more spot beams 1104 a, 1104 b (or, e.g., theborder of spot beams 1 and 7 in FIG. 10), the subscriber terminal 512may have a tendency to transition back and forth between respectivechannels associated with the two spot beams 1104 a, 1104 b and/orbetween coverage areas of the terrestrial and satellite systems. Inorder to prevent such a back-and-forth transfer between the channelsassociated with the respective spot beams, the present inventionadvantageously utilizes hysteresis so that there is, for example, apredetermined threshold (e.g., 2 dB) difference in signal strengthbefore allowing the subscriber terminal 512 to make such a transition.

The present invention also optionally utilizes negative hysteresis to,for example, balance the loading between the satellite and terrestrialcomponents and/or respective portions thereof. For example, with regardto FIG. 10, consider the case when a channel is being reusedterrestrially, and the channels of spot beam 7 are being used much morethan the channels of spot beam 1. Even though the channels of spot beam7 may have a weaker signal strength than the channels of spot beam 1,subscriber terminals 512 may be directed to terrestrially reuse channelsfrom spot beam 1 rather than spot beam 7 to, for example, better balancenetwork loading. It should be understood that negative hysteresis canalso be applied to a single satellite when the satellite containsmultiple frequency bands.

Negative hysteresis can also be used to balance loading between two ormore satellites 516 a, 516 b. For example, with regard to FIG. 11,suppose satellite 516 a has all or substantially all of its channelsused, and satellite 516 b has none or very few of its channels used.Then, even though the signal strength of channels from satellite 516 amay be stronger, it may be desirable to assign a call to satellite 516 bwhen, for example, RSSI is sufficient. Now, suppose channels fromsatellite 516 b have a stronger signal strength (relative to one or moresubscriber terminals 512), and that fewer of its channels are beingutilized. In such a case, it may be desirable to terrestrially reusechannels from satellite 516 b to, for example, balance network loading,even though the use of such channels may result in higher interference.

FIG. 13 is a high level flow diagram of illustrating the static anddynamic channel assignment features of the present invention. Asdiscussed in Channel Assignment Schemes for Cellular MobileTelecommunication Systems: A Comprehensive Survey, IEEE PersonalCommunications Magazine, June 1996, I. Katzela and M. Naghshineh,incorporated herein by reference, when channel assignment schemes areclassified based on separating co-channels apart in space, three broadcategories can be identified: fixed channel allocation schemes (FCA),dynamic channel allocation schemes (DCA), and hybrid channel allocationschemes (HCA). FCA schemes partition the given serving area into anumber of cells and allocate the available channels to cells based onsome channel reuse criterion. DCA schemes pool together all theavailable channels and allocate them dynamically to cells as the needarises. Consequently, DCA schemes are capable of adapting to changingtraffic patterns. HCA schemes provide a number of fixed channels, and anumber of channels that can be dynamically allocated.

If the satellite 516 has a geosynchronous orbit, the angle of arrivalfrom all spot beams is almost the same. In such a case, as indicated bydecision step 1302, the pool of channels can either be assigned to, forexample, a sub area of a spot beam and/or a terrestrial cell ahead oftime (i.e., fixed assignment), or assigned dynamically. In the case of ageosynchronous orbit, the signal strength measured by a subscriberterminal 512 using either a fixed or dynamic channel assignment schemeshould be substantially the same, since the geographical location of theGSSs 504 are fixed and the angle of arrival from a single satellite 516from different spot beams is substantially the same. Optionally, the GSS504 can be used to collect measured signal strength reported by thesubscriber terminals 512. Even in the case, for example, of a fastmoving vehicle that is handing off, channel assignment can be done by aESC 520 since, if the angle of arrival is fixed, then all the spot beamswill behave substantially identically.

If it is determined at decision step 1302 that a FCA scheme is beingused, then a preassigned channel is utilized at step 1304. The NOC 508,508 a, 508 b will generally determine whether a hybrid method isutilized, although a BSC 510 in conjunction with a GSS 504 can alsostore such information. The present invention can utilize either auniform allocation, in which the same number of channels are allocatedto, for example, each cell or subcell, or a non-uniform allocation, inwhich different numbers of channels can be allocated to, for example,each cell or subcell.

If it is determined at decision step 1302 that channels are assigneddynamically, a determination is made at decision step 1306 whether ahybrid method is utilized. If a strictly dynamic scheme is beingutilized then, a determination is made at decision step 1308 whethercalls are allocated on a call-by-call basis. If so, a subscriberterminal 512 can compute the signal strength of available channels, andselect the channel based on relative signal strength. If it isdetermined at decision step 1308 that channels will not be allocated ona call-by-call basis, channels may optionally be allocated based on pastand present usage patterns. For example, consider a situation in which60% of satellite channels are currently utilized and 40% of terrestrialchannels are utilized. Without considering past usage patterns, it wouldbe desirable to allocate the call to a terrestrial channel, since ahigher percentage of terrestrial channels are available. However, ifdata stored at a MSC 508, for example, indicates that terrestrialchannel usage in this cell it typically 80% (or 120%) and satellitechannel usage is typically 40% (or 20%), the system 500 may assign thecall to a satellite channel, even though it currently has a higherpercentage of its channels being used since, based on past data, it isexpected that traffic patterns will shortly return to their typicalloads (e.g., 80% of terrestrial capacity and 40% of satellite capacity).

Further, the system 500 can control dynamic channel allocationassociated with steps 1312 and 1314 in either a centralized ordistributed manner. In a centralized DCA scheme, the MSC 508, forexample, could maintain a centralized pool of channels (e.g., frequencybands) and allocate channels to calls based on, for example: the firstavailable channel; to minimize blocking probability; and/or to maximizesystem utilization by maximizing channel reuse.

The system 500 could also utilize a distributed DCA scheme in whichchannels could be allocated based on locally available informationavailable at, for example, each BTS 514. Some variations of distributedschemes include: a) allocating the first available channel; b)allocating the channel that minimizes adjacent channel interference;and/or c) allocating the first available channel that also meets someadjacent channel interference criterion.

If it is determined at decision step 1306 that a hybrid scheme will beutilized, the system preferably assigns a ratio of fixed and dynamicchannels to, for example, each cell, subcell or area of coverage. Theratio of fixed to dynamic cells generally determines the performance ofthe system. Optimal ratio is likely to depend on a number of factorssuch as, for example, system traffic load and/or system characteristics.At step 1316, channels are preferably assigned in accordance with, forexample, channel and system 500 load balancing and/or received signalstrength considerations.

FIG. 14 is an exemplary flow diagram of the call initialization processwhen the terrestrial mode is preferred and the satellite and terrestrialcomponents share a common portion of a frequency band as shown, forexample, in FIGS. 6 b, 6 c, 6 f and 6 g. A user places a call, forexample, after acquiring a control channel, and depressing a send buttonon the mobile phone/subscriber terminal 512, and requests a channel atstep 1402. At decision step 1404, a determination is made whether thesubscriber terminal 512 is a dual mode (satellite-terrestrial) terminal.If the subscriber terminal 512 is dual mode, then signal strengthmeasurements are made, for example at a BTS 514 and/or a GSS 504 of atleast a portion of the available channels (if any) that can be usedterrestrially at step 1406, preferably with one or more satellites 516and one or more associated BTSs 514. If, as determined at decision step1408, a channel is available for terrestrial use, a channel is assignedto the BTS 514 for terrestrial communication at step 1410 and the callis deemed successful at step 1414. If, as determined at decision step1408, all terrestrial channels are currently being used, a channelcurrently being used by a satellite 516 is assigned to a BTS 514 forterrestrial reuse at step 1412, and the call is deemed successful atstep 1414. It is preferred that the channel currently being used by asatellite 516 having the weakest signal strength be assigned to a BTS514 for terrestrial reuse.

If, at decision step 1404, the subscriber terminal indicates that it isa single mode terminal (e.g., a satellite terminal), a determination ismade by, for example, NOC 506, 606 a, MSC 508, 508 a, and/or RRM 720,720 a, at decision step 1418 whether a channel is available forsatellite use. If so, a channel is assigned for satellite use at step1416, and the call is deemed to be successfully established at step1414. If, at decision step 1418, a determination is made that a channelis not available for satellite use, the subscriber terminal 512 and/orsystem 500 wait(s), preferably for a predetermined time, beforedetermining whether a channel is available for satellite use at decisionstep 1418.

The method of FIG. 14 can be used not only for initial selection offrequencies as discussed above, but also for handoffs between channelswhen a subscriber terminal 512 travels, for example, from one area orportion thereof of satellite or terrestrial system coverage to another.As used herein, handoff refers to reassignment of a call to a differentchannel as a result of current channel degradation, and can be, forexample, intra-cell/intra-satellite and/or inter-cell/inter-satellite.Channel degradation can occur, for example, as the subscriber terminaldistance from the serving BTS increases or as a result of increase inco-channel interference Handoff schemes are designed to prefer handoffcalls to new calls when allocating channels so as to maintain anestablished connection (e.g., avoid dropping a call), and are preferablycompared based, for example, on the probability of successful handoffcalls and/or new call blocking.

Following are exemplary principles on which handoffs can be based: a)reserving some channels in each cell for handoff calls (i.e., GuardChannel Scheme); b) queuing up candidate calls for handoff (i.e.,Handoff Queuing Scheme) with or without guard channels; and c) queuingup new calls instead of handoff calls.

Since channels are set aside for handoff, the guard channel schemeincreases the probability of handoff calls. With a handoff queuingscheme, calls are queued for handoff when the received carrier powerfalls below a threshold. Queuing schemes can be, for example,first-in-first-out or priority queuing schemes. Priority can be basedon, for example, how fast the threshold is being reached.

For example, with regard to FIG. 10, if a subscriber terminal 512 goesfrom cell 1 to, for example, cell 7, the subscriber terminal 512 willscan the channels associated with each cell, and preferably select firstan open channel for terrestrial use, if one is available. If nochannel(s) is available, then the subscriber terminal 512 takes signalstrength measurements of the channels, and preferably selects thechannel having the weakest signal strength (from the satellite 516 andrelative to a subscriber terminal 512) for terrestrial use.

FIG. 15 shows an exemplary flow diagram of call initialization whenterrestrial mode is preferred and discrete satellite and terrestrialfrequency bands are utilized as shown, for example, in FIGS. 6 d and 6e. As shown in FIG. 15, at step 1502 the user places a call and requestsa channel.

At step 1504 the subscriber terminal transmits to the system whether itis a single or dual mode (satellite-terrestrial) terminal. Thesubscriber terminal can transmit this information on, for example asignaling channel. For example, the subscriber terminal can send acontrol signal upon powering up the unit to, for example, a BTS 514and/or satellite 516 indicating whether the subscriber terminal issingle mode or a dual mode terminal.

At decision step 1506, a determination is made by, for example, the BTS514 and/or BSC 510, based on the signal transmitted at step 1504,whether the subscriber terminal is a single mode or a dual modeterminal. If the subscriber terminal 512 is dual mode, then at step 1508the system measures, for example, the signal strength of the satellite516 and BTS 514 channels received by the subscriber terminal, andreports such measurements to, for example, a BSC 510 and/or a MSC 508,508 a, 508 b. For example, in accordance with GSM technology, toinitiate call setup, a subscriber terminal sends a signaling channelrequest to the system using a random access channel (RACH). The MSC 508,508 a, 508 b, after considering signal strength measurements, informsthe subscriber terminal via a BTS 514 of the allocated signaling channelusing an access grant channel (AGCH). Then, the subscriber terminalsends the call origination request via a standalone dedicated controlchannel (SDCCH). The MSC 508, 508 a, 508 b, for example, then instructsthe BSC 510 to allocate a traffic channel (TCH) for the call. Then, thesubscriber terminal acknowledges the traffic channel assignment using,for example, a fast associated control channel (FACCH). Finally, boththe subscriber terminal and the BTS 514 tune to the traffic channel.

At decision step 1516, a determination is made whether a BTS 514 channel(i.e., terrestrial channel) is available. If so, a determination is madeat decision step 1526 whether a satellite channel is available. If so, arequest is made to utilize the satellite channel terrestrially at step1524, and the call is deemed successful at step 1530. If, at decisionstep 1526, it is determined by, for example, a MSC 508, 508 a, 508 b,that all satellite channels are being used, the weakest signal isidentified at step 1534, a channel is assigned to the subscriberterminal 512 such that the subscriber terminal 512 reuses that satellitechannel terrestrially, and the call is deemed successful at step 1530.

If, at decision step 1516, a determination is made by, for example, aMSC 508, 508 a, 508 b, that a BTS 514 channel is not available, adetermination is made at decision step 1520 whether a satellite channelis available. If a satellite channel is available, the call is deemedsuccessful at step 1522. If a satellite channel is not available, atstep 1518 the subscriber terminal 512 and/or system 500 waits,preferably for a predetermined time, before taking additionalmeasurements at step 1508.

If, at decision step 1506, the subscriber terminal 512 is determined tobe a single mode (e.g., satellite only) terminal, the system measures,for example, the signal strength of the satellite 516 channels, andreports such measurements to, for example, the MSC 508, 508 a, 508 b. Atdecision step 1512, a determination is made whether a satellite channelis available. If a satellite channel is available, the call is deemedsuccessful at step 1530. If a satellite channel is not available, atstep 1528 the subscriber terminal 512 and/or system 500 waits,preferably for a predetermined time, before taking additionalmeasurements at step 1514. As is the case with FIG. 14, the methoddescribed in FIG. 15 can be used both for initial selection offrequencies, as well as handoffs between channels when a subscriberterminal travels, for example, from one spot area or one terrestrialarea to another.

FIG. 16 shows an exemplary flow diagram of base station-to-base stationor base station-to-satellite handoff when the satellite and terrestrialcomponents share a common portion of a frequency band as shown, forexample, in FIGS. 6 b, 6 c, 6 f and 6 g. At step 1602, the system 500and/or subscriber terminal 512 verify that the RSSI or other signalstrength indicator or criteria is satisfied. Before establishing a call,the RSSI, for example, should be high enough for the subscriber terminal512 to establish calls. As previously discussed, the RSSI is a relativemeasure of received signal strength for a particular subscriber terminal512, and is typically measured in db/m (decibels/milliwatt).

At decision step 1604, a determination is made whether the subscriberterminal 512 is a single mode or a dual mode terminal. The subscriberterminal can transmit this information on, for example, a signalingchannel. For example, the subscriber terminal can send a control signalupon powering up the unit to, for example, a BTS 514 and/or satellite516 indicating whether the subscriber terminal is single mode or a dualmode terminal.

If it is determined at decision step 1604 that the subscriber terminalis dual mode then, at decision step 1606, a determination is made by,for example, a BSC 510 whether a neighboring BTS 514 provides, forexample, an acceptable RSSI. Other criteria such as, for example,network loading and/or balancing considerations, may also be used. Ifso, a request to handoff to the neighboring BTS 514 is made at step1608. At decision step 1610, a determination is made whether the BTS 514has capacity available. If so, a determination is made at decision step1614 whether there is an available channel (not being used by thesatellite). If so, a request to handoff to the available channel is madeat step 1624, and the handoff is deemed successful at step 1626.

If, at decision step 1614, a determination is made that all channels arebeing utilized, the weakest satellite signal is preferably identified atstep 1622. At step 1624, a request is made to reuse the weakestsatellite signal, and the handoff is deemed successful at step 1626. If,at decision step 1610, it is determined that there is no BTS 514capacity available, one or more subsequent requests are preferably madeat step 1608, as determined by decision step 1612.

If, at decision step 1606, a determination is made by the BSC 510 and/orMSC 508, 508 b that the neighboring BETS 514 does not have, for example,an acceptable RSSI and/or does not, for example, satisfy other handoffcriteria (e.g., network loading), or if, at decision step 1612 themaximum number of allowed handoff requests has been made, a request tohandoff to a satellite is made at step 1616. At decision step 1620, adetermination is made by, for example, MSC 508, 508 a whether a channelis available and, if so, the handoff is deemed successful at step 1626.If, at decision step 1620, a determination is made that a channel is notavailable, then the subscriber terminal 512 and/or system 500 waits atstep 1618, preferably for a predetermined time prior to requestinganother handoff at step 1616.

If, at decision step 1604, a determination is made that the subscriberterminal 512 is single mode (e.g., satellite only), then a satellitehandoff request is made at step 1616, after which decision step 1620 isexecuted as discussed above.

FIG. 17 shows an exemplary flow diagram of base station-to-base stationor base station-to-satellite handoff while using discrete satellite andterrestrial frequency bands as shown, for example, in FIGS. 6 d and 6 e.At step 1702, the system 500 and/or subscriber terminal 512 verify thatthe RSSI and/or other signal strength indicators or criteria aresatisfied.

At decision step 1704, a determination is made whether the subscriberterminal 512 is dual mode. The subscriber terminal can transmit thisinformation on, for example a signaling channel. For example, thesubscriber terminal can send a control signal upon powering up the unitto, for example, a BTS 514 and/or satellite 516 indicating whether thesubscriber terminal is single mode or a dual mode terminal.

If it is determined at decision step 1704 that the subscriber terminalis dual mode then, at decision step 1706, a determination is made by,for example, a BSC 510 and/or MSC 508, 508 b whether a neighboring BTS514 provides an acceptable RSSI. If so, a request to handoff to theneighboring BTS 514 is made at step 1708. At decision step 1710, adetermination is made by, for example, a BSC 510 and/or MSC 508, 508 bwhether there is a BTS 514 channel available. If so, a determination ismade at decision step 1716 by, for example, MSC 508, 508 a whether thereis an available satellite channel. If it is determined that a satellitechannel is available, a request to handoff to the satellite channelfrequency is made at step 1722, and at step 1724 the handoff is deemedsuccessful.

If, at decision step 1716, a determination is made by, for example, MSC508, 508 a that all satellite channels are being utilized, the weakestsatellite signal vis-à-vis the subscriber terminal is preferablyidentified at step 1728. At step 1726, a request is made by, forexample, MSC 508, 508 a to reuse the weakest satellite signal, and thehandoff is deemed successful at step 1724. If, at decision step 1710, itis determined that a BTS 514 channel is not available, one or moresubsequent requests are preferably made at step 1708, as determined bydecision step 1714.

If, at decision step 1706, a determination is made by, for example, BSC510 that the neighboring BTS 514 does not have an acceptable RSSI, orif, as determined at decision step 1714, the maximum number of handoffattempts has been made, a request to handoff to a satellite channel ismade at step 1712. At decision step 1720, a determination is made by,for example, MSC 508, 508 a whether a satellite channel is availableand, if so, the handoff is deemed successful at step 1724. If, atdecision step 1720, a determination is made by, for example, MSC 508,508 a that a satellite channel is not available, then the subscriberterminal 512 and/or system 500 wait(s) at step 1718, preferably for apredetermined time, prior to requesting another handoff at step 1712.

If, at decision step 1704, it is determined that the subscriber terminal512 is a single mode (e.g., satellite only) terminal, a request tohandoff to a satellite channel is made at step 1712, after whichdecision step 1720 is executed, as discussed above.

The present invention also contemplates variations of the methoddisclosed in FIG. 17. For example, although FIG. 17 describes a processof first using terrestrial mode communications, and subsequently usingsatellite mode communications upon exhausting terrestrial channels, FIG.17 could also have first preferred satellite mode communications, andsubsequently use terrestrial mode communication upon exhaustingsatellite channels.

FIG. 18 shows an exemplary method of satellite-to-base station orsatellite-to-satellite handoff when the satellite and terrestrialcomponents share a common portion of a frequency band as shown, forexample, in FIGS. 6 b, 6 c, 6 f and 6 g. Upon determining that handoffcriteria (e.g., RSSI) is satisfied at step 1802, a determination is madeat decision step 1804 whether the subscriber terminal 512 is dual mode.The subscriber terminal can transmit this information on, for example asignaling channel. For example, the subscriber terminal can send acontrol signal upon powering up the unit to, for example, a BTS 514and/or satellite 516 indicating whether the subscriber terminal issingle mode or a dual mode terminal.

If it is determined at decision step 1804 that the subscriber terminalis dual mode, a request to handoff to a BTS 514 is made at step 1806. Atdecision step 1814, a determination is made whether the BTS 514 hascapacity available and, if so, whether there is an available channel atdecision step 1816. If so, a request to handoff to an available channelis made by, for example, MSC 508, 508 b at step 1808, and the handoff isdeemed successful at step 1810.

If, at decision step 1816, a determination is made by, for example, MSC508, 508 a, 508 b that all channels are being utilized, the weakestsatellite signal is preferably identified at step 1824. At step 1826, arequest by, for example, MSC 508, 508 a, 508 b, is made to reuse theweakest satellite signal, and the handoff is deemed to be successful atstep 1810. If, at decision step 1814, it is determined by, for example,BSC 510 that there is no available BTS 514 capacity, a request tohandoff to a satellite is made at step 1822. At decision step 1828, adetermination is made by, for example, MSC 508, 508 a whether satellitecapacity is available and, if capacity is available, the handoff isdeemed successful at step 1830. If, at decision step 1828, adetermination is made by, for example, MSC 508, 508 a that no satellitecapacity is available, then at step 1820 the subscriber terminal 512and/or system 500 camps on one or more of the channels that can be usedwith a satellite 516, preferably for a predetermined time, prior torequesting another handoff at step 1806.

If a determination is made, as previously described, at decision step1804 that the subscriber terminal 512 is single mode (e.g., a satelliteterminal) then, at decision step 1812, a determination is made by, forexample, MSC 508, 508 a whether there is satellite capacity available.If satellite capacity is available, the call is deemed successful atstep 1830. If, at decision step 1812 it is determined by, for example,MSC 508, 508 a that satellite capacity is not available, then at step1818, the subscriber terminal 512 and/or system 500 camps on one or moreof the satellite channels at step 1818, preferably for a predeterminedtime, prior to again determining whether satellite capacity is availableat decision step 1812.

FIG. 19 shows an exemplary method of satellite-to-base station orsatellite-to-satellite handoff while using discrete satellite andterrestrial frequency bands as shown, for example, in FIGS. 6 d and 6 e.Upon determining that handoff criteria (e.g., RSSI) is satisfied at step1902, a determination is made at decision step 1904 whether thesubscriber terminal 512 is dual mode. The subscriber terminal cantransmit this information on, for example, a signaling channel. Forexample, the subscriber terminal can send a control signal upon poweringup the unit to, for example, a BTS 514 and/or satellite 516 indicatingwhether the subscriber terminal is single mode or a dual mode terminal.

If it is determined at step 1902 that the subscriber terminal is dualmode then, a request to handoff to a BTS 514 channel is made at step1906. At decision step 1916, a determination is made by, for example,BSC 510 whether there is a BTS 514 channel available. If so, adetermination is made at decision step 1918 by, for example, MSC 508,508 a, whether there is a satellite channel not being used. If it isdetermined that a satellite channel is available, a request to handoffto that satellite channel is made at step 1908, and at step 1910 thehandoff is deemed successful.

If, at decision step 1918, a determination is made by, for example, MSC508, 508 a that all satellite channels are being utilized, the weakestsatellite signal is preferably identified at step 1926. At step 1928,the MSC 508, 508 a reuses the satellite channel having the weakestsignal, and the handoff is deemed successful at step 1910. If, atdecision step 1916, it is determined by, for example, BSC 510 that a BTS514 channel is not available, a request is made to handoff to, forexample, an adjacent spot beam or satellite at step 1924. For example,with regard to FIG. 11, if subscriber terminal 512 b requests a handoffto satellite 516 a and satellite 516 a does not have any availablechannels, subscriber terminal 512 b can subsequently request a handoffusing satellite 516 b. If, at decision step 1930 a determination is madethat an adjacent satellite (or spot beam) has an available channel, thecall is deemed successful at step 1912. If, at decision step 1930 adetermination is made that an adjacent satellite (or spot beam) does nothave an available channel then, at step 1922, the subscriber terminal512 camps on the current channel, preferably for a predetermined timebefore returning to step 1906.

If, at decision step 1904 it is determined, as previously discussed,that the subscriber terminal 512 is a single mode (e.g., satellite only)terminal then, at decision step 1914, if a determination is made that achannel from an adjacent spot beam or satellite is available, the callis deemed successful at step 1912. If it is determined at decision step1914 that a channel from an adjacent spot beam or satellite is notavailable, then the subscriber terminal 512 or system 500 camps on thedesired channel, preferably for a predetermined time, after whichdecision step 1914 is repeated.

As shown in FIG. 20 a, the present invention advantageously andoptionally implements an inverse assignment of the channels. That is, inat least one embodiment of the present invention, channels are assignedto the satellite component from one end of the frequency spectrum, andchannels are assigned to the terrestrial component from the other end sothat maximized spacing of channels is used. FIG. 20 a collectivelyrepresents the respective downlink 602 and uplink 604 frequency bandsof, for example, FIG. 6 b. For example, with regard to 602, 604 of FIG.6 a, assume that the channels are arranged from 1, 2, 3, 4 . . . 98, 99,100, from lower to higher frequency. The BTSs 514, for example, could beassigned channels 100, 99, 98, etc. from higher to lower frequencies,and the satellites can be assigned channels 1, 2, 3, etc. from lower tohigher frequencies. We have discovered that this scheme advantageouslyreduces the chances of reuse. When no channels remain for eithersatellite or terrestrial use then, as previously discussed, thechannel(s) having the weakest signal strength is preferably reusedterrestrially.

When there is a predetermined frequency closeness a BTS 514 is usingchannels 52 to 100, and a satellite 516 is using channels 1 to 49), thepresent invention also enables transitioning channels to avoidinterference and/or reuse. For example, channel 49 may be handed off,for example, to channel 2, assuming channel 2 is available (as indicatedby (2) in FIG. 20 b). Similarly, BTS 514 channels may also be similarlyhanded off.

Accordingly, in this additional feature of inverse frequency assignment,the MSC 508, 508 a, 508 b, for example, actively monitors the activechannels in ends of the systems (satellite/terrestrial,satellite/satellite, terrestrial/terrestrial, etc.) and proactivelyand/or dynamically re-assigns channels to maximize spacing between thesystems.

The many features and advantages of the invention are apparent from thedetailed specification, and thus, it is intended by the appended claimsto cover all such features and advantages of the invention which fallwithin the true spirit and scope of the invention. Further, sincenumerous modifications and variations will readily occur to thoseskilled in the art, it is not desired to limit the invention to theexact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention. While the foregoinginvention has been described in detail by way of illustration andexample of preferred embodiments, numerous modifications, substitutions,and alterations are possible without departing from the scope of theinvention as described herein.

For example, one embodiment of the invention focused on reusing orassigning terrestrial frequencies based on the status of or signalstrength of the satellite frequency. The present invention is alsoapplicable in the reverse. In addition, the present invention isapplicable to a plurality of satellite systems and/or a pluralityterrestrial systems having similar operational characteristics asdescribed herein. The present invention is equally applicable to voiceand/or data networks.

1. A system comprising: a detector that is configured to detect a firstsignal strength that is associated with a first wireless communicationschannel; and a transmitter that is configured to radiate electromagneticenergy over the first wireless communications channel responsive to thedetector having detected that the first signal strength is sufficientlyweak, wherein the detector is further configured to determine whether ahandoff should be made to a second wireless communications channelhaving a signal that is weaker than a signal of the first wirelesscommunications channel.
 2. A system according to claim 1, wherein thedetector is at the transmitter and/or spaced apart from the transmitter.3. A system according to claim 1, wherein the first wirelesscommunications channel is used by a satellite to provide space-basedcommunications and wherein the transmitter radiates electromagneticenergy over the first wireless communications channel to provideterrestrial communications.
 4. A system according to claim 1, whereinthe first wireless communications channel is used by a terrestrialsystem to provide terrestrial communications and wherein the transmitterradiates electromagnetic energy over the first wireless communicationschannel to provide terrestrial communications.
 5. A system according toclaim 1, wherein the first wireless communications channel is used by awireless communications system to provide wide-area communications andwherein the transmitter radiates electromagnetic energy over the firstwireless communications channel to provide local-area communications. 6.A system according to claim 5, wherein the transmitter provideslocal-area communications based upon a Time-Division Duplex (TDD) airinterface protocol.
 7. A system according to claim 6, wherein the TDDair interface protocol uses the first wireless communications channel totransmit and to receive information.
 8. A method comprising: detectingby a detector a first signal strength that is associated with a firstwireless communications channel; radiating by a transmitterelectromagnetic energy over the first wireless communications channelresponsive to detecting that the first signal strength is sufficientlyweak; and determining whether a handoff should be made to a secondwireless communications channel having a signal that is weaker than asignal of the first wireless communications channel.
 9. A methodaccording to claim 8, wherein the first wireless communications channelis used by a satellite to provide space-based communications and whereinthe transmitter radiates electromagnetic energy over the first wirelesscommunications channel to provide terrestrial communications.
 10. Amethod according to claim 8, wherein the first wireless communicationschannel is used by a terrestrial system to provide terrestrialcommunications and wherein the transmitter radiates electromagneticenergy over the first wireless communications channel to provideterrestrial communications.
 11. A method according to claim 8, whereinthe first wireless communications channel is used by a wirelesscommunications system to provide wide-area communications and whereinthe transmitter radiates electromagnetic energy over the first wirelesscommunications channel to provide local-area communications.
 12. Amethod according to claim 11, wherein the transmitter provideslocal-area communications based upon a Time-Division Duplex (TDD) airinterface protocol.
 13. A method according to claim 12, wherein the TDDair interface protocol uses the first wireless communications channel totransmit and to receive information.
 14. A method according to claim 8,wherein the detector is at the transmitter and/or spaced apart from thetransmitter.